Hi Christian,
I've actually heard of this situation happening before with your exact combination (LabVIEW Run-Time Engine 6.1 & Netscape web browser). This situation arises when you:
-install Netscape
-install LVRTE 6.1
-uninstall Netscape
-try to uninstall LVRTE 6.1
If I remember correctly, the best way to resolve this was to reinstall the original version of Netscape and then uninstall the LVRTE 6.1. My hunch is that you probably had a different version of Netscape installed when you originally installed the LVRTE 6.1. If you could figure out what version of Netscape was originally installed, install it, and then uninstall the LVRTE, you should be good. I've also heard of being able to make changes to the registry to fake it into being able to uninstall, but I'm not sure exactly how to do that...
Hope this helps,
Travis H.
LabVIEW R&D
National Instruments