mathcal in dcpic

Hello everyone,

I hope this is the right place to ask this; I am using dcpic in LaTeX and I have a comm. diagram (square) where I would like to put a \mathcal{F} as an object. If I do that, LaTeX gives some error. Do I need to load some package or something? Thanks in favor.

P.S.:What I see:

\GenericError ...
#4 \errhelp \@err@ ...
l.36 \obj
(4,1){$\mathcal{G}_1$}
.