Can't Save Test Results?

For some bizarre and unknown reason, I started getting the message "Can't save results of the run since ResultFilePath is null" when I was trying to run a test through the VSTS Test Manager. A quick Google search revealed the suggestion that a ResultFilePath element be added to the PropertyGroup tag in your solution file. That didn't have any affect for me.

It turned out that my testrunconfig file went missing. It can be added to the solution by right-clicking on the solution in Solution Explorer and adding a new item. Still, when I added the testrunconfig file back into the solution, the problem still existed. What it took was to close and reopen the solution along with adding the testrunconfig. Now life is good once again and testing can continue.