That dll was created by Acton Research and was not posted to the NI website. If you want to obtain that dll, you need to contact Acton Research.
Here is their contact information:
http://www.acton-research.com/contact.shtml
That dll is probably from their SpectraSense Software package :
http://www.acton-research.com/prod_spectrasense.shtml
Ray K
National Instruments Applications Engineer
