Cannot get compcln.exe to work to clean up winsxs directory

I am trying to free up disc space on a Vista PC using compcln.exe to clean up the WinSXS directory and make Service Pack 2 permanent. However, when I ran it, it failed to do anything and everytime I try to re-run it, it fails – I think there is a message saying it has already run and cant be run again, though it flashes off the screen too quickly to read. Any ideas how it can be re-run or any other way of cleaning out the WinSXS directory safely? Thanks