(In this case, being unable to submit the form at all is actually the best outcome, because it clearly tells the user that something is wrong while stopping them from doing any damage.)
For example, I once tried to create an account on such a website. The account creation form asked for your login name and your password; I picked a login and left the password field blank, assuming that either the system would spit an error at me or it would create a random password. Instead, it created the account with a blank password, which it turned out wasn't supposed to be possible, and various bits of the site were not too usable as a result. Including the password change form.
Unsurprisingly, I haven't really been back since.
An amusingly truthful hostname
We got email today from a machine called 'server1.ghettowebhosting.net' (IP address 220.127.116.11).
It was advance fee fraud spam. Truth in advertising strikes again!
(I have to wonder about the mindset that makes anyone name their business something like that. Especially when they are apparently a branch of 'Complet-Inet', and say they have multiple data centers with OC-48 connections; this doesn't sound too 'ghetto' to me. Of course, their front page also advertises '99% gaurantee uptime' [sic].)