I found this command and it allowed me to install easily

setup.exe /ACTION=AddNode /INSTANCENAME="MSSQLSERVER"

taken from the bottom of this thread:

http://social.msdn.microsoft.com/forums/en-US/sqlsetupandupgrade/thread/13a256b0-b95b-46a7-92d5-17a0b763f8dd/

Another work around for this is to uninstall the 2008 support files after each node install and let the installer reinstall them clean for each node (instance) added.

Hi all,

I have installed SQl server2008 twice on my machine. when I installed for the First time some components was missing. So I installed second time but by mistake I installed with another instance name. As i have Windows7 installed on my machine there is some compatibility issue with SQL server2008. I have downloaded the service pack for that and tried to install it but getting error:

TITLE: 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 'UMESHSQL2008' during configuration for features [SQL_Replication_Core_Inst,SQL_Engine_Core_Inst,MPT_AGENT_CORE_CNI,SQL_FullText_Adv,Analysis_Server_Full,RS_Server_Adv,]. In order to apply this patch package (KB968369), you must resolve any issues with the previous operation that failed. View the summary.txt log to determine why the previous operation failed.

Error code 0x84B20001.

Please help me why this is happening..

Thanks