Error when "Create New Site" as user in MarketPress.

I have found myself as the "User" on my multisite network. Subsequently, I will create a new page in the "My Sites" on my dashboard. When I chose my site name and my "Blog name" and press "Create Site" i get this message.

Fatal error: Class 'WP_Filesystem' not found in / home / Alberte / public_html / wp-content / plugins / blogtemplates / blog template files / copier.php on line 342

Why is that?

Best, Tim