How to save files on a jumpdrive?

I have been able to save all types of files on my Lexar 258mb Jumpdrive until recently. Every time I try to save a file it returns a message "unable to create file". I still have over 150mb of available space. I can open files on the drive and save them, but I cannot add any new file. Regardless whether it is a .doc file or .mpeg or other media. I have scanned for virus and found nothing. Any Suggestions??