SEP with IPS enabled was blocking Nessus scanning.

Solution: I had to add the host IP of Nessus scanner on the IPS excluded hosts and re-run the scan.

Solution: I had to add the host IP of Nessus scanner on the IPS excluded hosts and re-run the scan.
Server Group->Policies-> Intrusion Prevention->Edit Intrusion Prevention Policy->Intrusion Prevention->Excluded Hosts->Add IP Address of Nessus Scanner->OK