Thanks for replying. I should have stated in the original post that the flash drive is about 1/5th full. There's plenty of free space left. I did save my work on another flash drive and it worked fine, which means, I guess, that there's an error on the flash drive. Someone suggested that I copy everything to a file on my PC, reformat the flash drive and load all the files back into the flash drive and see if that solved the problem. What do you think?