My Nike GPS app quits on launch every time! Help!

I have the Nike+ GPS app, and it has worked fine for almost a year, but a few weeks ago it wouldn't let me log in to sync my runs anymore, and today it stopped working entirely, quitting on startup every time... any ideas what I can do to fix an app that quits on startup all the time?

I've tried deleting it, and installing it again, but that just made me loose my saved runs, so I restored my phone from a backup, and now the app is there and should contain my data, but it quits on startup!

Also tried resetting the phone...

thanks for any help!