Try taking a look at this knowledgbase document:
http://digital.ni.com/public.nsf/websearch/7E1C5C280E608A3A86256D3B007BADCD?OpenDocument
It says that there is a problem with building executables that contain VISA in LV 6i, but that it should work if you upgrade to 6.02. It also has a picture attached of an error message that is generated. Maybe you should look and see if this seems to describe what you are seeing.
Good luck!