looks like you have simplebrush as active tool - instead of 3dsphere. no symmetry available for simplebrush, its a 2 - 2.5d brush.
to load/activate 3dsphere click on simple brushs icon, a palette with all kinds of tools/brushes will pop up, including the sphere3d - select that one - there you go
oops - i just realized that you have loadd the thread as a script. should make it even easier. 3dsphere should be made available as small icon in the tool palettes window - just click on it to make it the active one.
hope this helps
- juandel