My best guess is that if you did not have VS2005 on the machine when you installed Measurement Studio, the installer did not (could not) register the MStudio namespace with the help system. This would mean that H2Viewer does not know about the various help files that make up the MStudio help. So, if you open one help file and click on a link to a topic that is in another help file, H2Viewer can't find that other help file and you would get the error you are describing.
To see if this is what is happening: in H2Viewer, if you go to File>>Open Namespace, do you see NI.MeasurementStudio.2005 in the list?
The only way I know to work around the issue is to figure out what file the topic is in and open it manually. You can figure out what topic a file is in by looking at the URL for the topic. The file will be indicated in the URL path segment immediately following "NI.MeasurementStudio.2005". For example, the following link indicates that the topic is in NINETDAQmxConcept.HxS: ms-help://NI.MeasurementStudio.2005/NINETDAQmxConcept/XML/Using_NINETDAQmx.html.
David Rohacek
National Instruments
