When I try to upload an image to the gallery, I get the error message, image not found, also, I can't seem to delete the 'non image,' in question.

You will probably have to furnish more detail. Not much to go on from the above. Look at the forum rules for some of the info we might need. But atleast give us more details on the error like where it shows up, the exact text, just the one image or multiple images....