Do you have multiple versions of LabVIEW on the same machine? If so, make sure they are installed in different directories. If you installed LabVIEW 6.0 to the same directory without uninstalling a previous version of the software, you could run into issues like this.
If you do not have a previous version of LabVIEW on your machine, this sounds like a corrupt installation. I would recommend uninstalling and re-installing LabVIEW 6.0.