This hit me tonight. I was pulling back off rollup 2 of Exchange 2007 sp2 as I was having a bit of weirdness in the office and to troubleshoot I wanted to pull back off the one update I had added last week. Fortunately prior to doing this I had spotted this thread —
Where the person pulling off rollup 2 had noted that it left behind a mixture of sp2 and rollup 2 files in the OWA premium directory. If you roll back, OWA no longer works and you get a “!” on the web site and you can’t click around the page. Basic works. Premium OWA doesn’t.
If you then find the Exchange 2007 sp2 that you left behind on the box (which I did) and drill down into the setup\serverroles\clientaccess\owa\forms\premium folder and then copy that over to the same Program files\Microsoft\Exchange\ yadda yadda folder on the c:\ drive (clicking on yes let me have access because UAC is blocking you as necessary) and copy and replacing those files in that folder as he describes, OWA is back fixed.
As he said, note that 1/2 of the folder contents ends up not being cleaned up and left with rollup 2 versions rather than rolling back to the proper one.
By the way, bookmark that Exchange software update forum as it’s always a great one to lurk and spot any issues with Exchange rollups BEFORE you install them.