Try rebooting the LANDesk(R) Management Gateway Service on the LDMS Core and rebooting the LANDesk Remote Control Service on the workstation. Then try running the %ProgramFiles%\LANDesk\LDClient\BrokerConfig.exe on the workstation, when you do are you putting the %USERID%@%yourdomain% in the LANDesk User field and your password?
Also you can go to the registry key on the workstation and view what the issuer has: HKLM\SYSTEM\CurrentControlSet\Services\ISSUSER ImagePath and the value could be: "C:\PROGRA~1\LANDesk\LDClient\issuser.exe /b /lx.x.x.x /SERVICE" where the x.x.x.x could be your IP. If so change it to "C:\PROGRA~1\LANDesk\LDClient\issuser.exe" /SERVICE and try it again.