Sadly for many months (I think since March) PayPal has had a severe intermittent bug in their web servers which sometimes kills payments and other web requests. I spent quite a bit of time integrating PayPal into my server only to discover that all too often my test payments crashed. The nature of the bug is that their cookie has a memory size leak and grows until you get a system error message. I and others have reported the bug to PayPal and they recommend clearing cookies to fix this it, but this is only a temporary fix. I strongly advise against using PayPal and recommend choosing some other payment company. my 2c.