As if there are not enough oddities and issues with a typical SSRS implementation, I ran into an interesting issue the other day where a customers SSRS reports just stopped working one morning when they came in. So the day before all reports were working properly with no issues and had been for some time.
When the user would go to run any of their reports they would get the following message
I began to dig into the issue a bit and everything is the environment looked good. There were no strange errors, services stopped, etc. From the surface everything looked to be running correctly.
The other strange thing I noticed was that all the report specific items were gone from the drop down menu in the library
After looking at some other areas I began isolating my testing to a single WFE server at a time since there was a load balancer in play in the environment. After doing this I quickly found that one of the WFE servers still worked normally, while the other WFE server exhibited the faulty behavior.
In the end, this problem was being caused because the SSRS SharePoint Add In had not been installed on one of the WFE servers. After installing the Add In all the reports ran normally again as they had been from either one of the servers.
SSRS 2012 Report Server Add-In
http://technet.microsoft.com/en-us/library/gg426282.aspx
http://technet.microsoft.com/en-us/library/gg426282.aspx
