Loox's pocket PC?

Operating system windows mobile
Excel mobile keeps sending out this message each time I update an existing Excel file adding information.
An error occurred saving 'Phone book'.
I have to copy and paste the whole file to a new excel file and save it including updates. I then open the new file, and as a test, add more information, and again the message appears and won't save the updated version unless its coppied to another file. What could be causing this?. Thanks in hope for solution replies.