serving mercurial from apache, push gets error 500

[Bill Barry]

I woke up this morning and one of my coworkers is having difficulties 
pushing to a shared repository that we are all using. I can push and 
pull from it just fine, but he gets an error when pushing (he can pull). 
What can we do to fix his push?

His prompt looks like this (url, username and password removed):
c:\work\stellar-hg\Trunk>hg push
pushing to https://******
searching for changes
abort: HTTP Error 500: Internal Server Error