As noted in the error dialog, the first step is to execute a RECONNECT on the console session from the root node of the console.
If you're unable to reconnect to the server, then we'll need to investigate further as to why the server is unavailable. The most common reason is that one or more of the requisite services are not running.
If the console reconnects then you should retry this certificate distribution task.
If it fails again, that may indicate that the WSUS Server registration for one of the target WSUS servers, or the Extension Pack registration, is defective. Try distributing the certificate to one target resource at a time to isolate which resource is triggering the error. If it's a WSUS server, then remove the WSUS Server from the Update Services node, and reregister that WSUS Server using the Update Services Registration Management tool. If the misbehaving device is the Extension Pack server, please send an email to email@example.com with your availability to set up a GoToMeeting session to further evaluate the situation.
If the distribution to the servers works correctly, then retry the distribution to client machines. If you were attempting to distribute to a WSUS Target Group, it's possible this is a manifestation of either a console connection failure or the WSUS server registration failure. Re-registering the WSUS server should resolve this issue; if not, please email customersupport.