[TYPO3] Typo3 Backend, Page tree has disappeared!

[Tapio Markula]

Rod Naugler kirjoitti:
> Hey all,
> 
> Just tried logging into my typo3 backend to work on some content and the
> page tree has disappeared. Logs in fine. Left menu is fine. Right intro
> is fine. CLick on Page and the center page tree area is blank.

generally reason is some plugin, which is incompatible with current 
version of Typo3.
Enable error messages (set error level '1' instead of '-1' using the 
install tool) to see what is wrong