Hi Roger,
AC3D's stl support is ASCII ( not binary-stl). Could this be the problem here?
I know a number of our users use Cut3D e.g. GreaseTattoo
http://www.inivis.com/forum/showthread.php?t=4236. There may be others on the Vectric forum.
Let us know how you get on (and post some of your results
).
Andy