I really can;t work this one out...

If i create any subdiv shape, even a basic primitive, and select Subdiv Surfaces>Texture>Planar Mapping all i get is

Error: Current selection doesn't match required selection type.

How can that not be a subdiv surface?? Oddly if i select auto mapping it splits all the uv sections up anf flattens them successfully, but i only want planar mapping. anyone know why this is happening?

Thanks, apologies if this has been asked before