ga2000gt, go to plugin management in your acp, there find the plugin
Andreas hint 3 click on edit and see the executionorder 126
go back and edit the plugin
Improved Thread Preview 1.5 change it's executionorder to something higher than 126, or change the executionorder of "Andreas hint 3" to let's say 4

If this still wont help, you can deactivate this plugin alone to see your threadpreview again, but keep in mind:
then you will have all hidden content in the preview.
emmanuel, some more information would be great,
what vbulletin version? what exact errormessage is showing?
'sid