Error when new users sign up using Pro Sites

Hello,

I am using Pro Sites and New Blog Template with no free option (Pay to Blog). I have a few users who have signed up but not complete the Pro-Site payment. When I login to their dashboard there is the following alert:

"ERROR: The themes directory is either empty or doesn’t exist. Please check your installation."

During the signup process I require them to select a blog template. Has anyone had any experience with this error?

Thanks,
Chris