Any other invalid characters I'm not aware of???

[pthok]

Hey y'all -

I have a membership site where people pay to join. Once in a rare while, a user registers, their credit card payment goes through but there is no record of them in my database. I think it has to do with an invalid character they entered into the fields. So before submitting the data to the database, I check for the usual suspects ("--" double dash, ";" semicolon, "'" single quote). Are there any other characters I missed. Or maybe I'm missing something and the problem is being caused by something else. Has anyone else experienced this? I'm running mysql 4.1 I think.

Thanks for any help.