[graph-tool] running graph-tool from inside matlab

Hi, I'm trying to run graph-tool from a matlab (Matlab2007a) under ubuntu 7, but I'm running into problems. I've added /usr/local/bin to the matlab path, but keep getting the same error -see attached. To run an unix command from matlab you type

...

unix(cmd)

Where cmd is, e.g. 'ls'. This works fine, but when cmd='graph-tool' I get the attached error. Has anyone tried this before? Many thanks, Rui