WSUS3 SP2 Install Failure (Error 0x80070643: Fatal error during installation)

Troubleshooting

I was trying to install WSUS 30 SP2, in preparation for Software Update Role installation in newly built SCCM 2012 SP1 Environment. As you may know WSUS 30 SP2 is prerequisite for SUP Role install. Install was failing irrespective of my method, either using Server Manager "Add Roles" or executing downloaded setup file WSUS30-KB972455-SP2-x64.exe, both were failing without revealing much info on GUI when install wizard throws message "Fatal Error". Bit of search around the logs revealed the root of cause o failure, post resolved underlying issue, install went well.

Actions Required to find underlying cause

Based on the way chosen to install, you would find WSUS Setup logs in %TEMP% which usually resolves to C:\Users\UserID\AppData\Local\Temp (In case of execution of downloaded file) or c:\Windows\Logs\ServerManager.log. These logs would give you the actual or more detailed information to find the root of install failure . In my case I used downloaded exe hence I found them under C:\Users\UserID\AppData\Local\Temp

WSUSSetup.log  : Main Log file that logs overview of install this gives generally very minimal info, hence you may need to rely on WSUSSetupmsi***.log which details each and every action of setup, is found in same folder as this file.
2013-01-18 15:43:39  Error     MWUSSetup          InstallWsus: MWUS Installation Failed (Error 0x80070643: Fatal error during installation.)
2013-01-18 15:43:39  Error     MWUSSetup          CInstallDriver::PerformSetup: WSUS installation failed (Error 0x80070643: Fatal error during installation.)
2013-01-18 15:43:39  Error     MWUSSetup          CSetupDriver::LaunchSetup: Setup failed (Error 0x80070643: Fatal error during installation.)
2013-01-18 15:43:53  Error     MWUSSetup          DoInstall: Wsus setup failed (Error 0x80070643: Fatal error during installation.)

WSUSSetupmsi_130118_1541.log: This log file has all information of setup actions and writes to another log for certain results, in this case it has written to WSUSCa_130118_1541.log which is also found in same location as this log
Error 1722. There is a problem with this Windows Installer package. A program run as part of the setup did not finish as expected. Contact your support personnel or package vendor.  Action ExConfigureDb….. C:\Users\UserID\AppData\Local\Temp\2\WSUSCa_130118_1541.log"

**WSUSCa_130118_1541.log: This log has given clue that it fails to install as setup cannto create Database file as same file already exists
**Cannot create file 'C:\Program Files\Microsoft SQL Server\MSSQL10_50.MSSQLSERVER\MSSQL\DATA\SUSDB.mdf' because it already exists. Change the file path or the file name, and retry the operation.Msg 1802, Level 16, State 4, Server IN-MUM-CM12POC,  Line 2
CREATE DATABASE failed. Some file names listed could not be created. Check related errors.

Actions Required Resolve the "How-To"

Though I don't remember how this file pre-exists, but guess I had earlier attempted either individual WSUS install or part of SUP roles install. So, post deleting the MDF and LDF files, reran the setup and this time WSUS Install ran successfully.