PDF File "NOT Valid win32 Application" for" My Documents" Double C

Operating System : Microsoft Windows Me

Problem: Upon Double Clicking on "My Documents" Icon I a get a list
of my files. ( OK )

When I Double Click on a PDF file such as xx.pdf I get the following error
message :

" c:\ MyDocuments\xx.pdf is not a valid win32 application "

If I Double Click on the Acrobat Reader 5.0 Icon the reader comes up OK and
I can "Open" file xx.pdf using the browser window. ( this works OK )

How do fix the error described above Re : win32 application ??

Thanks,
Dr. H.Mak