I worked with Jorge to resolve his problem and I would like to report here on the results for the benefit of other users.
- The initial problem was caused by incorrect install. The database table was not installed because he had not gone to Site Administration and clicked on Notifications. This was caused because he was using Notepad to read the README.txt, WordPad displays the file correctly.
- There was also a bug caused by the require_login() in return.php. This, under some circumstances, was redirecting the user back to return.php after a login causing a missing parameter error. I have taken out the function, which is not needed and put in a simple notice() which brings the user back to the desired course after payment.
Additionally I have added Spanish translations (thanks to Jorge) and a translated README.txt (also thanks to Jorge).
Also, if Moodle uses a Spanish UI, I request 2Checkout to display a Spanish UI as well.
I also would like to note that all testing has been done with "Direct Return" set to NO. I would be happy to test with "Direct Return" set to YES, but I do not have access to a non production 2Checkout account with that setting. In theory that would lead to a more robust setup. I would be happy to work with anyone who wishes to use that setting to test and fix any issues that might appear.
More info in the download (http://download.moodle.org/download.php/plugins/enrol/twocheckout.zip) in README.txt.