"An error has occured" after registration

When new users registrer onto my Gallery 2 installation, it seems to work because I can see them awaiting my authorization in the "Registration" page (in the admin section), but they get an "An error has occured" message after they click on the submit button. This error is A) ugly and B) misleading, because users keep registering again, thinking it didn't work the first time.

What can I do about it?

Nicolas

Gallery version (not just "2"):2.2.4
PHP version (e.g. 5.1.6):5.2.6
PHPInfo Link (see FAQ):
Webserver (e.g. Apache 1.3.33):2.0.63
Database (e.g. MySql 5.0.32):5.0.51a
Activated toolkits (e.g. NetPbm, GD):GD, NetPBM
Operating system (e.g. Linux):FreeBSD
Browser (e.g. Firefox 2.0):Firefox 2