Mongrel Error causing '500' Server errors

That problem has nothing to do with mongrel. Its a problem with your
session handling code. 95% of the time that people get the marshal
data too short error it's caused by storing too much data in the
session. Or storing complete AR objects in the session. If you are
storing full AR objects in the sessions then change your code to just
store the id in the session and do a lookup on that id in a before