"Having session timeout and security key problems at PayPal checkout"
I have four simple Buy now PayPal buttons.
My clients are still facing the same problem... they state that the "security key does not match message" and/or getting the "your session timed out" error... These errors have been reported to PayPal and they have not been very helpful with there automated replies.
I did pay someone to do this exact job and they were not successful... I believe the problem is at there (PayPal) page, not mine... I guess you need a script which can adjust visitor's browsers to clear history and cookies or something of that nature.