Sometimes this happens when a JPEG is used as a texture... but don't fret... everything will be saved from your last save (so save often, especially before you render)... you'll just have to recreate everything from that point onwards... Make sure to delete your AxiFFFe files that are created when this happens... as they consume hard drive space. And whatever you do... find another texture JPEG if this was the case. Cut your losses and close the file... something will be there when you open it again... but the generic error message will be gone. Sometimes right-clicking on the AxiFFFe file and renaming it '.br5' will take care of the problem... but not in my case. Good luck with this.