Test controllers are not visible or marked offline in MTM when multiple versions of MTM are installed

Details a known issue where Test Controllers appear offline in Microsoft Test Manager (MTM) when multiple versions of Visual Studio are installed on the same machine, and a newer MTM version attempts to connect to an older Test Controller. The issue is caused by assembly version conflicts. Workarounds involve using assembly redirection in `mtm.exe.config` to point to the correct assembly versions or using the older MTM client to connect to the older Test Controller.