This is probably something previously addressed, but I have found nothing via the search or after scanning the first 10 or 11 pages of threads, so here goes nothing.
I just bought an XBox One and Forza 5. After installing everything and waiting for the downloads and updates to complete, I played the first race series. I then took the opportunity to upgrade my car before moving on to the next career series. When I try to select any of the possible race series, they give me a pop up that says the content is not installed. When I back up and try to select a different league, I get the same message on every option. In the dashboard the game indicates it is fully downloaded and installed. Can any one tell me what is going on here?
Crud, there was something like this on the old forum. I’ll see if I can find it for you. Might take me a bit to find it, but I’ll let you know either way.
Very interesting… I have had my share of “snags” since the launch in Nov., but I haven’t heard of this. If I find something out, I’ll let you know… Sorry about your probs… 
Update 1: First, before anything else, try exiting the game and hard rebooting the system (aka holding the shining Xbox logo until it turns off and then turning it back on) if you haven’t already.
Second, not exactly what I was looking for, and the links are broken, but if reboot didn’t work then this might be relevant while I keep looking:
"Troubleshooting
For slow installations, Xbox Support suggests installing while disconnected from your network. See these instructions.
For problems with crashing or hangups, these may be resolved by installing and reinstalling the game (which will not erase your gamesave from the Cloud), or resetting your game profile (which will erase your game progress and start over). To reset your gamesave, relaunch the game and at the splash screen, hold both triggers and bumpers down while pressing the Y button, then confirm. See these instructions."
(Note: The resetting the profile thing likely doesn’t apply here. Re-installing may however.)
Update 2: Ok, sorry to say, I’m not finding what I’m looking for. I take pain meds at night for a bad leg, and tonight’s got taken shortly before I read this thread. Lol, I am now official reaching the point of no longer being helpful I’m afraid. If this doesn’t get taken care of before tomorrow, I’ll look again, but I’ll have to call it quits for now. Good luck. Hopefully it’ll get sorted before then.
I did a hard reboot last night before I went to bed. This morning everything seems to be working properly. Thanks for the help!
Great! I was just getting set to get back to my search, and checked back here first. Glad I did. More time for games now. XD
Glad to hear it’s working now. Enjoy. 
Good to hear,Ironwolf,enjoy!
Good that its working properly for you now enjoy the game.