In looking around at other posts on this topic, I followed their advice and tried:
1) changing themes to the twenty-eleven theme.
2) Disabling all but the s2member plugin.
Neither of these worked, so I don’t see how this could be the result of interference with the shortcode parsing. And as I said in the original post, I have not changed anything or updated the theme or other plugins recently.
I checked the API log (paypal-api.log). Bots seem to hit the button all the time (?) though they never complete a transaction, so the last “success” in the log was Thu Mar 14, 2013 8:40:05 am UTC:
LOG ENTRY: Thu Mar 14th, 2013 @ precisely 8:40 am UTC
PHP v5.2.17 :: WordPress® v3.5.1 :: s2Member® v130221
Memory 38.44 MB :: Real Memory 38.75 MB :: Peak Memory 38.55 MB :: Real Peak Memory 38.75 MB
www.nasarracenia.org/join/
User-Agent: Mozilla/5.0 (compatible; Baiduspider/2.0; +http://www.baidu.com/search/spider.html)
The first error was Thu Mar 14, 2013 6:19:59 pm UTC:
-------- Output string/vars: ( Thu Mar 14, 2013 6:19:59 pm UTC ) --------
array (
'__error' => 'Error. Please contact Support for assistance.',
)
There is nothing different between these two attempts not even a day apart. All of the button parameters remained the same and the website did not change, nor did our paypal settings. Hence my complete and utter confusion.
Anyone have a guess or another possible solution I could try?