No response returned by Paypal

I have setup, as per instructions but when making a test payment in Production, it returns me to this message - "No response returned by Paypal".

Return url contains:

order_process?amt=1.00&cc=GBP&cm=3&st=Completed&tx=*********** (this number is returned properly, I have just not added it here)
Hi. Do you have a PDT token filled in and properly enabled in your Paypal account? If you look at the logs/ folder you can find paypal_pdt_last.log. Send it to tim (at) and I will look at what happend with the http request.
I only have a paypal_ipn_last.log?
and yes, I sorted the PDT.
Hmm.. that's concerning. There should always be a log when the pdt request is initiated. Does it happen every time or just this once?
Every time and no file with the name you state
The tx variable is definitely being defined by Paypal, on return.
My bad the request should be logged in logs/http_request_last.log. Can you send that file, unless it's been overwritten by some other call.
Sent via email
Any luck?