A site tree's XML structure must not be empty

[Rick Barter]

I was trying to get Gems to work ..... and then found when I try to 
login to admin site or connect remotely I get:

"Sorry! there was an error: Server configuration error. A site tree's 
XML structure must not be empty.

the error was detected by Frontier 9.0 in mainResponder.respond "

How can I fix this problem?

Can I restore from backup?

I have all sites backed up.

thanks,

Rick  Barter
Conners Emerson School
Bar Harbor, ME