Unable to verify POST vars

[ChuckNorris]

After paying for a membership at PayPal, members receive the following error (and do NOT get a registration email).

"ERROR: Unable to verify POST vars. Please contact Support for assistance.

This is most likely related to an invalid PayPal® configuration. If you
are the site owner, please check: s2Member -> PayPal® Options."

I verified the settings over 20 times, and everything is perfect. I do not have sandbox testing on, and I never had a sandbox account in the first place.

Here are my stats:

WordPress Version: 3.0.1
PHP Version: 5.2.9
Operating System: Linux
Apache Version: 2.0.63

I saw a few threads about this issue and I uploaded the 3 curl and fopen files and tried browsing to them. All of them fail, but I'm not sure what that implies.

Any ideas?

Thank you!

[ChuckNorris]

Can someone please help...

[ChuckNorris]

????