sorry, my instructions were wrong, Sam has it right.

The pz2 file should look like this at the start

{
version
    {
    number 4.01
    }
figure
    {
    material    material_name

        {

etc

where material_name is one of the materials of your figure.

if you are using compressed files you cant edit them in this way. It must be an mc6 file to pz2 file type.