Like Uberchic said, please post any issues at the official project page here: http://drupal.org/project/referralsources/. I can't promise I'm ever going to look at this page again.

It's odd that I don't see this error. Maybe it has something to do with the version of MySQL I'm running. The title field had the "not null" flag set but also had default value set to null. I would expect it to give me the same error you're getting, but it seems to implicitly convert the default null to an empty string on insert. I'll get this fixed in the next release. For now, just set the default value of the title column of the referralsources_submissions table to an empty string or unset the "not null" flag and it should work fine.