Welcome to Focus Fanatics! This is a relatively common issue, usually the product of one or two issues. One issue is that moisture may be getting into your shift linkage and freezing the cables. There is a write up here somewhere that shows how to test for that. The 2nd is your clutch fluid may be getting dirty. Some people have had better luck with the Motorcraft clutch fluid, but I can't vouch for that as I haven't done it.
Good luck, and welcome again!
ROTM June '13, PNW Crew #42, SR #245, Rally Rev #02