The 1.4.4 version now contains strong-named assemblies that are installed in the GAC. Unfortunately, this requires a recompile of your tests against the new Adapdev.UnitTest.dll. The reference location is still the same, so all you need to do is open your solution and rebuild.
If you don't recompile against the new Adapdev.UnitTest.dll, previous test assemblies will load with no tests.
If you want to maintain your current list of test assemblies (displayed in the Open Recent menu, or in assemblies.xml) then do the following:
Copy C:\Program Files\Zanebug\assemblies.xml to a safe location
Rename your copied file from assemblies.xml to assemblies.zanebug
Uninstall the previous version
Install the new version
Copy the assemblies.zanebug file from your safe location to C:\Program Files\Zanebug\ - this will overwrite the file that was installed there by default