Occasionally I run into image_gallery errors on saving.
usually, the problem is an orphaned image, without an ID. so check your DB for any images that aren't correctly related.
then, if you're still having issues, sometimes the order in which you install the modules seems to fix it:
delete all mentions of image and image gallery in the database.
then delete the 3 modules.
and re-installed them like this.
dataobject & uploadify
that usually fixes any problems i have.
probably an easier way though!