Using the 3.1 version of GAP I noticed the following:

On the one hand I get:

gap> A:=CharTable("Symmetric",6);;
gap> PermChars(A,6);
[ ]
gap> PermChars(A);
Error, Variable: 'mino' must have a value at
for <var> in [ maxu .. mino ] ... in
suche( 2 ) called from
Permut( tbl, arec ) called from
PermChars( A ) called from
main loop
brk> quit;

On the other hand I get:

gap> A:=CharTable("S6");;
gap> PermChars(A,6);
[ [ 6, 2, 0, 3, 0, 1, 0, 4, 2, 0, 1 ], [ 6, 2, 3, 0, 0, 1, 4, 0, 2, 1, 0 ] ]
gap>

Does a generic character table need to be reordered before
asking for permutaion characters?
If so how?