This sounds like an issue that was present in NI-DMM version 1.5. My suggestion would be to download NI-DMM 1.6 from our website and install this latest release of the software. Go here to download the software:
You should also be sure to uninstall the previous version of the driver through 'Add/Remove Programs' before installing the newer one. If you are already using NI-DMM 1.6, or if installing this version does not correct your problem, you should contact the National Instruments Applications Engineering department to receive free technical support. To initiate this process, go to www.ni.com and click on 'Technical Support'. There will be a link on the subsequent page (on the left hand side of the screen) for 'Request Support' which will allow you to beging the support process.