Ruah, I'll make a stab at it, since no one else has tried... But I have my doubts.
What operating system are you using? XP?
You might try removing the file-type association for ".mis" files.
1) Start Windows Explorer
2) In the menu bar choose Tools, Folder Options, File Types
3) Scroll down the list of Extensions until you reach "MIS" "MIS File"
(If you don't find an entry in the list for "MIS" files, then never mind.)
4) Click on the "MIS" "MIS File" row in the list to select it.
5) Click the DELETE button to remove this file type association.
Anybody got a better idea?
Good Luck
Stalwart