I retested but the problem is still the same. I am stuck to think of anything else I can do except wait for something to change on Paypal system or spend days trawling to find someting on the forums (which I've already done)! Without access to CB Subs code I can't debug step by step what is happening or change the information being sent to Paypal.

If you can investigate further I would be grateful. If your testers wanted to recreate the problem I could backup the sri-connect test site you used (I use Akeeba Backup) and send the whole site to you. Or I'm happy for you or your testers to access our site and perhaps try using one of Joomlapolis's Paypal Sandbox testing accounts as a payment gateway to see if that works ( if it did that would at least isolate the problem to something set-up on the Paypal accounts I created).

For the moment I have devised a workaround by changing the error message that is shown by CB Subs on return from Paypal. This now says the payment was completed and the subscription will be applied shortly - my client will then in CB Subs back end tick that subscription in the users record and delete the basket (to stop an invoice appearing each time). Not ideal but it works (except no record in back end of payment and the end user may have to wait a day or so to get access to extra functionality). As the actual payment is processed by Paypal ok then my client thinks it is workable for the short term.

For the longer term could you please respond to my later points in my last post about whether Joomlapolis could develop a bespoke payment gateway for a UK merchant service provider and what I would need to do to get this done?

I know other posts mention an API for custom payment gateways is in development - is this due for release in the near future?

The point at which the process is failing as far as I can see is after CB Subs has received the IPN/PDT Notification, when it is trying to send back a response in order to then get a verified confirmation from paypal.

As I don't have the code for CB Subs I thought I'd try a non-commercial extension which supported paypal sandbox and IPN processing which I could then step through the code to find the point at which I could not send a response back to paypal. I chose Maian Media a music store application.

Unfortunately this works perfectly with paypal sandbox, receiving IPN and sending the response and then receiving the verified confirmation from paypal.

Now I know this is different code but it shows that intrinsically there is nothing wrong with how my hosting is set-up that would in itself create problems in Paypal IPN. Changing host is not an option anyway as we are entirely happy with our hosting company.

As we have paid for CB Subs I would like this to be escalated so that someone with detailed knowledge of the actual code in the paypal processing module (cbpaidsubscriptions.paypal.php) can provide details of what would cause the Communication Error. The message must be generated at one or more specific points in the code. Details of what those points are may help to identify what in my set-up is causing the error (is it cURL, openssl, some specific parameter?). If this support is not available I would request that you provide me with a decoded cbpaidsubscriptions.paypal.php file (and any ones linked to from this) so that I can debug this problem e.g. by setting trace on cURL.

Well after much investigation and then a bit of luck the problem with CB Subs not handling Paypal PDTs/IPNs has been solved, although I can't give an exact cause for the problem!

As part of some other work I had asked my hosting company to rebuild Apache on my VPS server. After the rebuild the site wouldn't come up at all. Eventually the hosting company identified that some of the RPM's used in the rebuild, and some in the previous build, were corrupted. After refreshing the RPMs database and rebuilding Apache my site was back on line and miraculously CB Subs and Paypal were now working (it also solved a problem I reported on the forum about not being able to set up encryption on a Paypal CB subs Payment Gateway).

So as we thought it was something at my server that was not working with CB Subs. Unfortunately because the hosting company didn't identify individual RPMs and their corruption I am no wiser as to what exactly didn't work.

Hopefully enhancements in CB SUbs 1.1 and later releases will improve the error reporting. With encrypted software, as with compiled software, it is vital that error messages and/or error logs provide sufficent information to actually diagnose problems rather than employ guess work and just trying turning things on or off.

Thank you for your support.