Windows firewall being enabled is a common cause.
2. This issue can also occur if a NAT is in place. Windows RPC/DCOM connections are have problems NAT'ed connections. This is a problem that is native to Windows and can be worked around in the following ways:
i. Move the PS server to the same side of the NAT device as the server being discovered to avoid the NAT altogether.
ii. Manually discover the server and import the results into the PlateSpin Client.
Microsoft has published technical articles on how to limit the port range for DCOM and RPC:
Using Distributed COM with Firewalls
How to configure RPC dynamic port allocation to work with firewalls
DCOM Does Not Work over Network Address Translation-Based Firewall