remote control error

When I remote control to a workstation (the computer object and IP
address are correct), I got the following message:

Still trying.. Possible reasons for delay include slow link, agent not
running or wrong network address stored in workstation object.

I have removed the Zenwork 3.0 server from the tree. I thought when the
computer object is created in NDS, I don't need the zenwork server for
remote control to work. Could someont tell me what service is required.
The reason I removed the server was this was also our backup server and
we have installed the backup program onto another server. We only use the
remote control for Zenwork and we are looking at upgrading Zenwork to 6.5
so I though I don't have to reinstall Zenwork 3.0 on this backup server.

Thanks
Che