I have had this with Lansweeper (and other programs that install websites).
The problem is that the installation programs seem to switch IIS 7 to 32bit compatability mode which breaks OWA.
If you switch IIS 7 back to 64bit mode then Lansweeper still works and so does OWA!
To switch modes open a command prompt and user the following:
Switch from x64 to x32
cscript c:\inetpub\adminscripts\adsutil.vbs SET /w3svc/AppPools/Enable32BitAppOnWin64 True
Switch from x32 to x64
cscript c:\inetpub\adminscripts\adsutil.vbs SET /w3svc/AppPools/Enable32BitAppOnWin64 False
I would love to know why programs do this when they install, any info from the developers?