Itunes not recognizing the Apple ID password? Any solutions?

It works on Apple Id.com but not with Itunes. I see posts to this issue since 2012!! I have been updating every possible application, system, etc. calling Apple support and not real solution. Now Apple is asking me to update to El Capitan. but I'm sure that has nothing to do with it, it I Tunes and Apple ID that do not seem to communicate correctly. Help please!!! I started 5 hours ago trying to get Uber... I'm still getting same message: update Uber, but you can't do it trough Itunes store.