Upgrade from Windows Server 2008 to Server 2008 R2 RC

I happened to be researching this same error code this morning, and came across this MSDN blog post that might help: How to overcome error 0x80070490 when installing updates in Windows Vista/Server 2008

I was not able to get it working again by following his step-by-step, but the following did:

1. Open %windir%\logs\cbs\cbs.log. You'll likely need to run Notepad as Administrator in order to view it.
2. Go to the bottom of the log and do a find for "Error", making sure you choose up for the direction

3. This should bring you to one or more errors like the following:

   2008-09-27 15:53:29, Error
   CBS Failed to resolve Package: Package_for_KB905866~31bf3856ad364e35~x86~~6.0.22.0. hr: 0x80070490

4. Do a web search for the KB number of the update that failed (KB905866 in this case), which should bring you to a Microsoft page where you can download the stand-alone installer for this issue's patch

5. Download and install the appropriate version (32-bit, 64-bit, etc.)
6. The next time you run Windows Update, it will recognize that the update was installed.

The first thing you need to do is establish why isn't the service starting. The SSAS service will log its problems into the system event log, and there is where you need to look. Start EventVwr.exe and check the application log for events reported by SSAS.

The errors are also reported in the error log files, see Analysis Services Configuration - Data Directories for their location.