Websignup & "Error while inserting event log into database"

[Insert usual newbie disclaimer here.] A page with nothing but "Error while inserting event log into database" comes up after about every other registration attempt using Websignup. The user is registered, however. I’m calling it uncached, so I don’t think that’s the problem. Any ideas? Thanks in advance.

Sounds like a system event logging error.
Inside the Manager go to Reports => System Events, see if anything is being flagged.