[FieldTrip] problem with clusterplot?

[veniero at med.unibs.it]

Dear FieldTrip  users,
I'm trying to run a cluster-based permutation tests on time-frequency
data. I get the result:
found 1 positive clusters in observed data found 0 negative clusters in
observed data, but I'm not able to use clusterplot because if the
following error:
??? Error using ==> ft_clusterplot at 171
no clusters present with a p-value lower than the specified alpha, nothing
to plot

Is this possible? Maybe it's just a trivial question.

Many thanks,
Mimma