[GAP Forum] Error computing a stabilizer in GAP 4.10.2

[Marc Keilberg]

I was interested in computing the automorphisms of a group sending a given
conjugacy class of subgroups to itself, when I encountered an error that I
can't make sense of.  It only affects one particular subgroup conjugacy
class, and none of the others, and I don't know why.

N := SmallGroup(81,14);
auts := AutomorphismGroup(N);
csubs := ConjugacyClassesSubgroups(N);;
T := csubs[5];

This is the class of the cyclic subgroup of order 3 generated by
N.1*N.2^2.  I try to compute the stabilizer as follows:

gap> Stabilizer(auts,List(AsList(T),AsList),OnSetsSets);
Error, Action not well-defined. See the manual section
``Action on canonical representatives''. at
/proc/cygdrive/C/gap-4.10.2-x86_64/lib/oprt.gd:440 called from
TestIdentityAction( acts, pnt, act ) at
/proc/cygdrive/C/gap-4.10.2-x86_64/lib/oprt.gd:833 called from
CallFuncList( StabilizerFunc, arg ) at
/proc/cygdrive/C/gap-4.10.2-x86_64/lib/oprt.gi:2874 called from
<function "Stabilizer">( <arguments> )
 called from read-eval loop at *stdin*:81
you can 'quit;' to quit to outer loop, or
you can 'return;' to continue


As I indicated, all other conjugacy classes of subgroups seem to work just
fine with the same code to compute the stabilizer.  So what's happening
here?  And, as an aside, is there a smarter way to get this sort of
stabilizer?

Thanks,
Marc