New site created with no template installed

Hi,

I have a Multisite with Marketpress & pro sites installed.

New user site are being created with a default twenty ten theme which I have deleted from the available themes.

The new site are therefore inaccessible (blank page )

I have selected Simple Market as the default theme which I thought would be auto selected on creation of new sites.

Should there be a setting somewhere to rectify this?

Thanks