Every time I have had this issue it was either:
1. Remote agent was not running on test machine
2. Windows firewall was enabled and blocking the RPC call from QC Server
3. QC server was unable to ping QTP machine because they were on different subnets. I don't think QC can use IP Address. It must have a name for the host, which also means your host must be DNS registered and your DNS query must be resolvable on the QC machine.
Hope this helps.
1. Remote agent was not running on test machine
2. Windows firewall was enabled and blocking the RPC call from QC Server
3. QC server was unable to ping QTP machine because they were on different subnets. I don't think QC can use IP Address. It must have a name for the host, which also means your host must be DNS registered and your DNS query must be resolvable on the QC machine.
Hope this helps.