I was attempting to install MS SQL Server 2005 Express edition without success on a computer run Windows Vista Business. There was an error message mentioned “…failed to compile the Managed Object Format (MOF)…” I’ve tried about five times with various solutions; still it didn’t fix the problem.

As always, I found a working solution when I was about to give up on this installation. The problem was that the WMI repository was corrupted. There are two ways to fix this: one is to reinstall the WMI, and alternatively you can repair it instead.

I opted for the 2nd option. Here is how you can do it. Run the command prompt (cmd) as the administrator. Then execute this command:

Wait for a lil while, you should see the following error message:

Then, re-execute the same command for one more time to finally repair the WMI repository.

Once you’ve finished the above step, try to reinstall the SQL Server 2005 Express edition again. Please be sure to install the latest version of the SQL Server Express edition which is the SQL Server 2005 Service Pack 2.

Source: SQL Server Setup error on Vista