Sure, just for reference though, I'm running windows7 home edition. So things might be slightly different if you're not.
1) Click on the windows button in the bottom left to bring up the start menu. At the bottom of this, I've got a little text box with 'search programs and files' in it. Type '.mission' in here and it'll search through your documents folder.
2) If that doesn't turn up anything, click on the 'see more results' bar. This should open up another window, at the bottom of which will be a header saying 'search again in'. Select 'computer' and it should then start a search of your HDD.
Obviously, this search may take a little time as it'll go through all your drives. But for me, it seems to find anything with the word mission in it. Hopefully, you should be able to locate the errant files