The setup has encountered an unexpected error while Setting Internal Properties. The error is: Fatal error during installation

During uninstallation of Microsoft SQL Server 2005 or uninstallation of Microsoft SQL Server Service pack, you may encounter the below error

"The setup has encountered an unexpected error while Setting Internal Properties. The error is: Fatal error during installation"

This generally happens when after the installation of SQL Server, the Machine has been promoted as Active Directory Domain Controller.  This also might occur due to SID issue as well or the SQL Server user groups do not match the corresponding security IDs in the Windows registry.

To resolve the issue and uninstall the SQL Server 2005 cleanly, couple of entries needs to be removed from registry. Make sure you take a backup of registry before you proceed.

A good KB is available on Microsoft to work around this issue.

http://support.microsoft.com/kb/919945