Exchange 2013 Error: Application\MSExchange RBAC (70)

Hello

We have introduced Exchange 2013 into our 2007 environment and are seeing an error on a Mailbox Server:

Event description: (Process w3wp.exe, PID 10024) Fail to create runspace for useruser because the user has reached the maximum number of connections allowed. Max allowed connections: 18.

I cannot find any information on this, does anyone have any?

Thanks

shapi