To sum up the above answers from myself and Austin and add a bit to it, try:
1) Checking that no widgets have been added (Make sure to look at the app's history in case someone committed a broken widget in)
2) Try to Sync the project directory on the modeler () - should sync the folder structure widgets with what's loaded in the project
3) If you can't sort it out with the above try re-downloading the project or as a final solution branch off from the last revision that ran successfully and see if that works successfully on your machine (you can backtrack from this version to your current version)
Hope this helps