Error:

An instance with the same name is already installed on this computer. To proceed with SQL Server setup, provide a unique instance name.

Snapshot:

Causes:

This problem may occur if one of the following conditions is true:

1. The existing instance of SQL Server 2008 is a unique named instance. However, you try to install SQL Server 2005 as the default instance.
2. The existing instance of SQL Server 2008 is a named instance, and you use the same name when you try to install SQL Server 2005 as a named instance.
3. The named Instance, you are trying to install is already present.

Workaround 1:

NOTE : In My case SQL INSTANCE  is “RELYONDB”

Click on the Start menu, choose Run and type regedit

Navigate to

• HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\

1.       Find “MSSQL$RELYONDB” , and delete

• Go to HKEY_LOCAL_MACHINE\Software\Microsoft\Microsoft SQL Server

1.      Remove “RELYONDB”  from the REG_MULTI_SZ value named InstalledInstance
2.      Delete the subhive named MSSQL.1
3.      Delete the subhive named  RELYONDB

• Go to HKEY_LOCAL_MACHINE\Software\Microsoft\Microsoft SQL Server\Instance Names\SQL

1.     Delete the value named  “RELYONDB”

• Go to c:\ drive

1.    Delete the folder %ProgramFiles%\Microsoft SQL Server\MSSQL.1

Restart the PC.

Use either Windows installer cleanup utility to manually remove all traces of MSSQL on your PC.

Re-run SQL installation

Workaround 2:

Try Installing SQl Server, with a different Instance name.