And this is what I see when getting into the frontend of litecart, which means that anyone can see it, too:

Warning: VQModObject::applyMod(product_reviews.xml) - Search not found in "": includes/templates/*.catalog/views/box_product.inc.php(1) [ABORTING MOD] in ~/vqmod/vqmod.php (Line 585)

Make sure the package of the addon you downloaded matches your LiteCart version.

I have not downloaded any addon recently and this warning is the result of a failed database update. 

So what would be the course of action in that case?

That's the problem right there. You upgraded your platform but did not download an updated version of the add-on that complies with the new version.

Go to this page and grab the one that complies to your new platform update:
[url=https://www.litecart.net/en/addons/79/product-reviews]https://www.litecart.net/en/addons/79/product-reviews[/url]

This article has some valuable information about upgrades:
[url=https://wiki.litecart.net/doku.php?id=how_to_upgrade]https://wiki.litecart.net/doku.php?id=how_to_upgrade[/url]

Tim, I will try to look into it closer but so far, having looked at PHPmyadmin and indeed there is no table called _product_groups so my guess is, perhaps just a shot in the dark, that one of your product_reviews addon updated might have had this CREATE TABLE query with all the necessary ingredients (_product_groups) and I must have missed it and now the litecart trying to upgrade the database from 2.1.5 to 2.2.0, having the product_reviews of pretty old version... what I am saying that one of your product_reviews addon version might have it and now the question is which one is it? If I am right in this reasoning, could you please tell me which update it was? Thanks!

Yes, so the one compatible with 2.1.5... it seems! Is it this one:

Version 2.1.1 | Uploaded 7 May 2018    Rewritten and updated for LiteCart 2.1.1   Compatible Versions: 2.1.1

Trying to run upgrade.sql from the penultimate product_reviews addon and here we have an error:

INSERT INTO lc_products_reviews_info (review_id, language_code, review)
SELECT id, language_code, review FROM lc_products_reviews
MySQL said: Documentation

1054 - Unknown column 'language_code' in 'field list'

If you are using LiteCart 2.2.0 then you should use Product Reviews 2019-11-04. If you click the [+] you should see all compatible versions.

When it comes to product groups it was removed in 2.2.0 in favour of attribute groups. The fact that it's missing in your installation is a sign that the 2.2.0 upgrade patches have been executed there. Restore your backup where you had product groups before attempting to run the upgrade again.

The part where you are missing language_code column is probably because you are using a newer version of the addon where it is no longer present.

I have just restored the backup and nothing is working now! HTTP ERROR 500 No idea how to proceed from here!

And here is the errors.log attached.

@tim I would appreciate your help as soon as possible because at the moment it does not look as if I could restore the shop back. You still have got the same login credentials I gave you a long time ago, if you would like to login into the shop (if that is possible, at all) and help.

I can assist you on an hourly charge.

Does this mean that your promise when I bought the add-on from you mean nothing? 

It was your suggestion to say to revert back to the backup of litecart, which I have followed and which resulted in this mess!

My promise? Are you referring to the Update Guarantee Program?

I don't know how you ended up with the problems you are having. There are continous reports of users successfully updating to LiteCart 2.2.0 so there is nothing broken in the platform or the upgrade patches.

I don't think there is anything wrong with my recommendation to revert your files and database to a backup. If you made a backup before things started to go wrong then you should be fine restoring it.

I provide free support in cases where users have a problem that might be the cause of a malfunction. I don't provide free support in cases where users are experimenting with their platform or doing things they not really know what they are doing. Or I would be working day and night for free.

Are you going to help or not? Your rude words only make things worse. I specialise in a completely different field and I don't expect you to know anything about my area of specialty. Yet, I don't despise you because of that, do I?

How was that rude? You broke your platform and you are pissed off at me that it's not working. Even more rude, you hold me responsible for something that is your own making. I don't even have to answer to you, yet I do it. Trying to help everyone out in the forums.

I gave you an advice to restore your backups to a point before things went wrong for you. And if you restored your files and database from a proper backup there would be no trace of any troubles. Yet you somehow messed that up too and now blaim me that a backup ruined it even more. That is not possible in the concept of what a backup does. Either you didn't make a proper backup or you didn't properly restore it.

If you wreck your car, do you go hold your car dealer responsible for telling you to take the car for a spin? I am not responsible for what you do.

I followed your advice here to the letter. I am not a professional in this field and that's what I do. I have not been trying to experiment with the system as you have implied.

1. I upgraded the litecart using Softaculous, making a backup. The database upgrade has failed.

2. I turned to you for help and after some exchange of information here you told me to restore the update and that is what I did, using Softaculous again. The backup was restored successfully, according to Softaculous, yet the store is not working.

That's the whole story so I don't really know what could have gone wrong.

Did your backup restore both files and database or just the database? It could be that you restored the database for 2.1.x but you are using files for 2.2.0. Or the opposite. Somehow there seem to be an inconsistency after your backups were restored. I am assuming your backup was made before all this trouble started.

I will look into this on my return to England tomorrow, at this time abroad with only mobile phone to use.

I think Softaculous might have gone somehow wrong... but I have no idea how. I did backup both files and the datebase and trying to restore it just failed. How can I possibly get it fixed?

OK, here we are again. Despite the backup version not working, I decided to try to upgrade the same way I did last week and it is funny but I managed to get to the same point, with the upgraded litecart but the same errors for the database and vqmod. Then I did /install/upgrade.php, like you suggested and I got the scrambled version again... not working, at all.

So, going back to the backup version again, upgrading with the same errors, etc. but what can be done now not to scramble it with the /install/upgrade.php?

Follow up: no real progress, just the same message...

Upgrading system to 2.1.6...

Upgrading database to 2.2.0... Fatal error: 1146 - Table 'aristos_lite233.lcvt_product_groups' doesn't exist INSERT INTO lcvt_attribute_groups (id, date_updated, date_created) SELECT id, date_updated, date_created FROM lcvt_product_groups; in ~/includes/library/lib_database.inc.php (Line 248)

... and the front end and back end of the store work but not fully functional, so the store is not working, really.

If the table lcvt_product_groups was not present in your backup then you must have made the backup after you ran the 2.2.0 upgrade. That table is not removed until you run the 2.2.0 upgrade patches. In this stage the 2.2.0 upgrade patch tries to extract info from the table before it is going to remove it. But it is already removed so the upgrade halts. The upgrade patch expected that if you are coming from 2.1.6 then this table would be present.

If you don't want to mess with the upgrade tools this wiki article I posted earlier has some alternatives: [url=https://wiki.litecart.net/doku.php?id=how_to_upgrade]https://wiki.litecart.net/doku.php?id=how_to_upgrade[/url]
I would do "How To Resume a Failed Upgrade" but you might want to go with "How To Recover a Broken Platform".

I don't know how much time you are spending with this. I could probably resolve it for you within an hour.

The backup was from the 2.1.5 version of the database, not 2.1.6, as it says in the error message. So the upgrade fails way before getting into the 2.2.0 version. Was the table lcvt_product_groups table there?

I will try to proceed with either of the routes you have pointed out but probably I don't have enough time to learn and focus on this for too much time... so I seriously would like you help, please!

Litecart is not a bad store solution and since I have been using it for a few years now, I have become used to it and I would like to continue. Over the past week of the store not working, I have been trying to find an alternative solution, testing other shop scripts but it seems that I am getting back to you :-)

Anyway, I would appreciate your prompt help as I cannot wait any longer... could you spend an hour to help me?

Sure can. I will email you some info.

If you like LiteCart so far it might be hard to find an alternative solution that suits your brain muscles. Hosting your own components has it's ups and downs. Most important is that you know your strings to pull.

Yes, sure. Awaiting your email message...