Hi
This behaviour can happen when installing Visual Studio .Net or ORCA because they install a newer mergemod.dll which isn't compatible with the older version that LV 6.1 uses in the Application Builder installer.
This steps should help:
1. Open a command prompt.
2. Change to the "\Program Files\Common Files\Microsoft Shared\MSI Tools" directory.
3. Execute the following command: "regsvr32 /u mergemod.dll". This should report that the unregister was successful.
4. Change to the "\Program Files\National Instruments\shared\Installer" directory.
5. Execute the following command: "regsvr32 mergemod.dll". This should report that the register was successful.
Hope this helps
Luca
Regards,
Luca