Mail won't allow attachments
------------------------------------------------------------------
Verify/repair your disk first (not just permissions), as described here:
The Repair functions of Disk Utility: what's it all about?
After having fixed all filesystem issues, if any, try this to determine the scope of the problem:
1. Go to Apple Menu > System Preferences > Accounts, and create a new user account for testing purposes.
2. Either log out of your main user account or just quit Mail so that it does not interfere with the other user account.
3. Log in as the newly created user and set up Mail anew there.
4. If this is a POP account, go to Mail > Preferences > Accounts > Advanced and disable Remove copy from server after retrieving a message.
5. Check whether the problem also happens when logged in as another user.
20" iMac, Mac OS X (10.5.6)