I recently started getting this nice error every time that I tried to open the ECP site in my browser. I was pretty sure that it had always worked before, but this was clearly a problem now.
A little testing helped narrow down the problem. OWA worked fine. Users were not having any issues with email. Everything looked pretty good. So, I checked a few issues. I checked the properties of the ecp(Default Web Site) in the EMC Server Configuration level, and it was set appropriately. I tried to reset the virtual directory, and checked the logs.
As part of my troubleshooting, I wanted to eliminate the load balancer from the equation, so I went to the url, https://localhost/ecp, and it gave me a really interesting output.
This was the key to resolving the issue. The ‘MobileDevices’ is not a valid RBAC query error was the clue. The fix was simple. I opened up the Web.config file in \Program Files\Microsoft\Exchange Server\V14\ClientAccess\ecp\Troubleshooting and identified the allow roles section under the MobileDevices.slab tag in the xml.
I deleted the MobileDevices+ in the Web.config and saved it to get the below result. That was all that was needed to fix the issue.
After this, everything worked fine again. Thank you RU6 for being so helpful.