Quote Originally Posted by Catrin View Post
had my Jamis upside down at my mechanics advice
Did your mechanic tell you to store the bike upside down? Or is there some other reason?

A bike repair book I've read mentions that advanced bike mechanics work on bikes right side up, while beginning amateurs flip the bike over.

In your pictures, it looks like the derailleur is tugging on the chain. Shift it so that it isn't pulling the chain against a chainring. To unstick the chain, you'll need to gently tug, push, wiggle, and twist until you find where it is caught. Start by seeing if you can free the end of the chain going towards the rear derailleur. To get more slack chain, shift the rear to the small (likely 11 tooth) cog - you'll have to manually move the chain down the cassette.