New Coursepress Pro Install Shuts Down WP Admin

Today I installed CoursePress Pro on a site of my network. After running through the settings and installing the theme, checking my own theme and activating marketpress amongst other things, it stopped allowing me back into the backend. The front end was fine, but any attempt to edit anything displayed a blank page.

I deleted the site (its new) and reinstalled, but the same thing happens again.

I read it may have something to do with MarketPress, but on the last of 3 attempts I purposely didnt activate MarketPress and it still happened.

Any ideas appreciated. thanks
Paul