I was playing with TMG & Exchange 2010 publishing and had to delete TMG & associated SQL Express 2008 installation. When I tried deleting SQL Express 2008 from the control panel, I got the error message below.
Rule "Restart Computer" Failed. A Computer Restart Is Required. You Must Restart This Computer Before Installing SQL Server
I am not a SQL expert, but I had to delete the installation to start fresh. The solution was to delete a registry entry and I was able to delete the SQL install.
Launch registry and navigate to HKEY_LOCAL_MACHINESYSTEMCurrentControlSetControlSession Manager
Delete the key "PendingFileRenameOperations" (Don’t restart the server, as it will put the registry key back).
Re-run the setup again and all will be green.
Now that all showed green, I could successfully delete the SQL Express installation.