Look in the Program Files\LANDesk\Shared Files\cbaroot\certs and open the .0 file there. It has the gateway connection information. If it still has the old information there try replacing that file with the one from the Core servers C:\Program Files\LANDesk\Shared Files\Keys directory.
Are you saying that both of these locations are on the core?
Sorry, No, the first location is on the client machine. The second is on the core. Take the one from the core and replace the client's .0 file with the one from the core.