So far this is the most promising and disturbing information I have found: https://www.x.com/thread/42018?start=0&tstart=0

It appears PayPal "updated" their site with code that broke a lot of application \ sites that use their services. They have told everyone the are working to resolve the issue and tried to offer workarounds. I still cannot produce the issue on my test site or this site. This also appears to be typical from what I am reading in these posts. I will implement one of the suggested workaround and post a patch. However, I cannot promise this will correct the issue at this time. I also am unable to verify that the problem is fixed since I cannot produce the problem. Please post the exact settings you are using and a link to the page with this module that produces the error. This may help me to reproduce the error on my test system and verify the workaround has solved the problem.

Again I apologize for the trouble you have had with this module and strongly encourage you to read the forum thread at the url included in this post. It may shed some light on the difficulties in corrected the issue sooner.

Thank you again for your patience and understanding as I work to find a solution to these changes at PayPal.

 Ahh ok now this is starting to make more sense. Some of the changes made from version 1.x to 2.x of the module may solve this problem for you. I am going to email you the install package for version 2 of this module. Please try it out and let me know. If at all possible, please attempt the install on a test system first and backup your live site BEFORE installing the new module. I do not anticipate any problems, but I certainly would not want to make things worse trying to rush a fix.

P.S. To everyone reading this, ALWAYS backup your DNN installation before installing ANY module! Yes this includes the ones release by the DNN core team!

Can I get you to email me the fix as well, please?

[EDIT - Removed Email Address]

Thanks!