OK, found out that I've introduced error messages on forumpages when the image wasn't found. So I ripped some more code from the old hack by Steve St.Lauren and added it to the new code by ggiersdorf.
Seemes it works fine now
Code:
Check the revised code in post #52
Note that I introduced two more phrases (image not found and imageserver offline). Feel free to use plain text instead. Otherwise, don't forget to add those (global) prhases