There is no evaluation of theme pathes saved in user preferences while login. If the theme directory is missing the user ends up in a broken page.
It's on my todo, I will built-in a function to check if the user set theme is still available and if not make a fallback to the configured default theme.
The Patch will follow today in the evening. ;-)
nocc broken theme
Logged In: YES
user_id=529507
Originator: NO
Fixed in CVS.
It'll be included in next release.
But you can download daily snapshots at :
http://nocc.sourceforge.net/download/
Thanks for the bug report.