Try deleting the email and have it resent to you, and attempt to open it again.
(Try sending yourself a couple different types of .pdf files and see if you could open any of them.)
If you still can't open it, I'd suggest updating to the latest OS. http://www.blackberryforums.com/gene...ilanguage.html
See if that fixes anything, if not then there is a setting that is turned on or off somewhere.