Hello,
It is certainly possible to call one .m file from another. The "MathScript using Riemann Zeta" example shows how to do this. The VI calls zeta.m which in turn calls eta.m. You will likely need to set the search path to tell LabVIEW MathScript where to find your .m files. Which version of LabVIEW are you using? In LabVIEW 8.5, you can set the search path for the MathScript node by going to Tools >> Options and clicking on "MathScript: Search Paths" in the Category list. Simply add the directories containing your .m files on the right side.
Grant M.
Staff Software Engineer | LabVIEW Math & Signal Processing | National Instruments