I just downloaded the most recent version (v1.2) that I use on Matlab2013b. (I also tried on Matlab2015b but the toolbox did not work well).

For an update, I think I found the reason of this error that is linked to the parallel processing. While I have the Matlab parallel toolbox, when I tell the GTG toolbox to compute the graph theory metrics on 2 or more cores, the error appears, but if I use only one core (no parallel processing), it works without any error...