Most probably the problem is caused by the 'Multiple allowed' option set to Yes for attribute StableOutfallProject. The system does not allow this in shortcuts because if there are multiple related object instances it would have no way of knowing which of the instances the shortcut should point to.
Go to the property dialog for attribute StableOutfallProject, un-check the 'Multiple allowed' box and save the attribute and the object. Then re-create the shortcut attribute. The problem should go away.
Let me know if it does not work.