RSRP-291223: "Could not build the projects. Tests will not be run" error prevents ReSHarper to run unit tests

I am getting the following error when running tests:

"Could not build the projects. Tests will not be run.
The build could not be started. Could not launch a Visual Studio build.
Operation aborted (Exception from HRESULT: 0X80004004 (E_ABORT)"

The tests run perfectly with VS Test runner, it is just R# they fail with.

Clicking "Run Unit tests" brings up the error dialog immediately, but in the background does also trigger a build, which finsihes successfully.

I have had this problem before and I fixed it by doing a VS repair. What seemed to bring on this new behaviour was adding a new config setting to my .testsettings file. The new config element was:

<ExecutionThread apartmentState="MTA" />

It doesn't appear to be anything with my test project; I created a new blank test project, totally standalone, I created the following unit
test:

[TestMethod]
public void TestMethod1()
{
	Assert.IsTrue(true);
}

Tried to run the tests via R# and still get the same error.

For some further information, last night after I reported the issue I did a repair of VS.Net as I said I would, and that made the problem go away.
However once again, as soon as I added the MTA apartment state config, the error came straight back again

<ExecutionThread apartmentState="MTA" />

And now again I'm at the point where I can't run any unit tests via R#.

Furthermore, the MS Test runner can run the tests, however the Test Results window seems garbled. Specifically I can see the five test result rows, however the cells appear empty. Scrolling within this window make the cell contents flash up sporadically.