It seems to me that for semidirect products of AG groups the operations
Embedding and Projection are not implemented.
(For permutation groups they seem to work.)
Here is an example:

gap> G:=AllSolvableGroups(Size, 64)[249];
grp_64_249
gap> N:=Subgroup(G, [G.1, G.4, G.5, G.6]);
Subgroup( grp_64_249, [ a, d, e, f ] )
gap> B:=Subgroup(G, [G.2]);
Subgroup( grp_64_249, [ b ] )
gap> phi:=IdentityMapping(B);
IdentityMapping( Subgroup( grp_64_249, [ b ] ) )
gap> GG:=SemidirectProduct(B, phi, N);
Group( g1, g2, g3, g4, h1, h2, h3, h4 )
gap> Embedding(B, GG, 1);
Error, Record: element 'Embedding' must have an assigned value at
return arg[2].operations.Embedding( arg[1], arg[2], arg[3] ) ... in
Embedding( B, GG, 1 ) called from
main loop
brk> quit;
gap> Projection(GG, B, 1);
Error, Record: element 'Projection' must have an assigned value at
return arg[1].operations.Projection( arg[1], arg[2], arg[3] ) ... in
Projection( GG, B, 1 ) called from
main loop
brk> quit;

As a workaround I use GG.embeddings resp. GG.projections.

Ralf Dentzer dentzer@kalliope.iwr.uni-heidelberg.de