I came across an interesting issue after my recent migration from Microsoft Project Server 2007 to Microsoft Project Server 2013. The migration was successful with a few errors that were due to the missing custom solutions. When I went to Project Center, Resource Center and Timesheet page after migration, the ribbon was disabled. I was not able to perform any operation through ribbon even when I selected a project, a resource or a timesheet.
We performed all sorts of troubleshooting including investigating event logs, ULS logs, verifying and escalating security privileges etc. etc. Performed a couple of hours of troubleshooting with no luck. Then we decided to verify this behavior in Microsoft Project Server 2010 environment. It had same behavior except on each Project Center, Resource Center and Timesheet pages, there was an error from another web part. This was not there in Microsoft Project Server 2013. After analyzing the error, we realized that the migration process had inserted duplicate web parts on all of those pages. For example, on the project center page, there were two instances of “Project Center” web part. A quick way to check duplicate web parts is by appending “?contents=1” [without quotes] to the page URL.
if you see two instances of a web part, just choose one and click “Delete”. Once the duplicate web part is deleted, Ribbon functions normally. Weird!! But I had a couple other similar experiences with ribbon and mostly something unusual turns out as a cause if the security is properly set up.