I think the problem is that the matlabpool was replaced by parpool. Therefore, matlabpool('size') is not valid anymore and parpool('size') does not do the job.
I found this quick fix here: https://github.com/RobotLocomotion/drake/issues/1009
if (matlabpool('size')==0) matlabpool; end
if isempty(gcp('nocreate')) parpool; end
For me it worked. Cheers!
P.S. Thanks Ben, new here!