It appears as if that file:
Cannot be found.
I looked for that file. It’s no where to be found. But it looks like it has a different version:
I copied the file name mentioned in the error message, changed both file names (both .cat and .mum, didn’t know if they need each other during installation) and tried installing again.
That Solved the problem:
I changed back the file names to their original names and restated the server – everything works fine.
Perhaps a Lync Server 2010 RU1 soon?