Hello Hubert,
You must have LabVIEW 7.0 or later to use Traditional NI-DAQ 7.4.1. I would recommend uninstalling Traditional NI-DAQ 7.4.1 and instead installing NI-DAQ 7.4.0, which is the latest version of Traditional NI-DAQ that can be used with LabVIEW 6.1. You can download all previous versions of the NI-DAQ drivers
here. More information about DAQ driver and LabVIEW compatibility can be found in the following Knowledgebase.
KB 3PIA89N5: NI-DAQ for Windows Support for Different LabVIEW Versions
Let us know if that solves the problem.
Travis G.
Applications Engineering
National Instruments
www.ni.com/support