There isn't any limit per-say, but I figure if you use some kind of gigantic file it could have trouble with it.
My guess is you saved to an improper format. Remember, jpeg... just jpeg, not interlaced, and no fancy crap. Also save as rgb, not cymk. These aren't requirements as such, but I've seen photoshop and various other image editors totally screw up a jpeg if any of those options are used.