I am modifying reports in Visual Studio 2015 Community, creating the .rdl file for upload to Dynamics CRM 2015 Build number 126.96.36.199.
I found a report dated 3/11/2014 (not been touched for a while) renamed it and uploaded it to CRM. This uploaded fine. I then attached this same report, to the solution in Visual Studio and changed the case of one letter in the report. I then saved the report, in Visual Studio and attempted to upload it to CRM. This failed with the above error message.