I'm trying to uninstall SQL Server Standard 2008 (my sandbox copy) using KB 955499 from my Windows XP 32-bit machine so that I can install SQL Server 2008 R2. Tried 5 times, rebooting between each try, but each time I get the error message:

Microsoft SQL Server 2008 Setup

The following error has occurred:

Value cannot be null.

Parameter name: sddlForm

This error occurs while attempting to uninstall SQL Server 2008 using Add/Remove Programs. Removal Progress is at Performing Windows Installer actions, SqlEngineConfigAction_remove_unconfigrc_Cpu32. SQL Services are all stopped. Also installed are Books Online for SQL 2005 and 2000, and SQL 2000 Enterprise Manager and Query Analyzer. I've done Google searches and searched Microsoft forums but don't see a solution. Thanks for your help.