Hi,
On the website of the mathworks,
http://www.mathworks.nl/help/matlab/ref/which.htmlthe function "which" can have multiple inputs. The help of the function "which" in freemat (at least in version 4.0) suggest that only the one input version is supported. I suspect that it would help to make a fuller implementation of "which". I couldn't find where "which" is used in arduino.m, so it's probably in a called function. If you can find out where "which" is called, and with what syntax, you've got the problem isolated.
Greetings,
Roger.