Which Petri Net toolbox are you using? The one that gets referred to most commonly, from Romania, offers a demo version that requires R2007a, and mentions a "full" version compatible with R2012b but I cannot find any method described of access that version. (I just now sent off a message to them asking them about it.)
There is also https://www.mathworks.com/matlabcentral/fileexchange/6501-matlab-petri-net-toolbox -- is that the one?
