Authentication Issue - No Popup Screen to Accept Remote Control Request

Having issue after keyed-in the username, password and domain (using AD authentication method), there is no pop-up screen or take more than 2 mins for the pop-up to appear at user site to accept the remote control request. The agent just saying Validating User... and forever until time out. I am using AD authentication method where the NS server is member server of AA domain, while the agent machine is member of BB domain and lastly the ID using for authentication is CC domain. Anyone having the similar setup and facing same issue? Thanks.