File extentions corrupted

I am getting this strange behavior on a Windows XP Home system. I installed
Acrobat 8.1 and MSOffice2003.
I get an email on AOL with a PDF attachment. When I open it the first time I
get an error message (something like "file not found"). After that, I cannot
run acrobat reader at all. A command prompt window appears briefly.

Something similar happens with MSWord.

I had to re-install these 2 applications every time this happens. The funny
thing is that it does not happen every time I receive an attachment.

Please help