[TYPO3] No thumbnails in BE

[Christian Lerrahn]

Hi,
this might be trivial but I still don't really know what the problem
is. When editors use content elements that involve images on one of my
TYPO3 sites, they will never see thumbnails. Now, I've had the problem
before that the thumbnails could not be generated due to configuration
problems. However, for one I remember a placeholder showing up in that
situation and then I also can't find any configuration errors when I
check.

Any other hints what could be going wrong or how to debug this?

Cheers,
Christian