SQL Server 2008 R2 cumulative update was giving an error stating SQL Server setup failure.

SQL Server Setup has encountered the following error:

A failure was detected for a previous installation, patch or repair for instance “MSSQLSERVER” during the configurtion for features………. Error code 0x84B20001

Found it on Microsoft forums and other posts to look for these registry entries:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Microsoft SQL Server\MSSQL10_50.MSSQLSERVER\ConfigurationState

MPT_AGENT_CORE_CNI
SQL_Engine_Core_Inst
SQL_Replication_Core_Inst

All REG_DWORD values were set to 3 and changed them to 1.

Wow, this time the setup validation succeeded and the SQL server 2008 R2 update operation was completed successfully.