Mold Tool with 2 parts?

Hi All,

I am trying to create a mold tool for two parts that are going in the same tool.

They are individual parts that I have combined in an assemly, given them the spacing and alignment I need to fit in the tool etc then saved as a solidworks part

Now I am in solidworks but cannot get the mold tools workflow to work.

The tooling split always remains greyed out?

Any help? Or further info required?

SolidworksPlastics And Mold Design