I had a previously working copy of a report project that opened fine in VS2012. A person on the team upgraded the project to VS2015 which began causing me trouble opening the project. It would say some of the projects were incompatible or that the project could not be loaded. It gave me the option to upgrade, which I tired and it failed.
I did several things.
At first I thought I did not have SSDT 2015 installed so I installed that, uninstalled that, ran a repair on VS2015, which resolves the project incompatible error on a couple of the projects but I still could not load the Report Project. I un-installed and re-installed different version of SSDT 2015.
I learned VS2015 comes with the SQL Server Data tools and I needed to update this item called "SQL Tooling" but it was hard to understand because nothing in Tool -> Extensions and Updates read precisely "SQL Tooling", I just ran anything that said it needed to be update and when the update ran it was labeled "...Tooling...". So that was confusing. I think the one I updated was Microsoft ASP.net and Web Tools or maybe Microsoft .NET Core Tools. After trying so many things to resolve the problem, you never know, you just know you got it working finally.
After doing all that, I reloaded the project again and continued to have the error: "... rptproj: error: There is an error in XML document (2, 2)."
I found a recommendation that said: Try deleting the "project.user" or "*.rptproj.rsuser" file located in the project folder. Reopen the solution.
And finally after hours of work, this solved for me although I had tried it early on and it did NOT work, so some combination of installed SSDT, uninstalling, updating and then deleting worked.
