To resolve this issue you have the following three options:
- Create an exception in the Windows 2008 firewall for the ports used by the two services only:
69 UDP (Altiris PXE MTFTP Server service)
4011 UDP (Altiris PXE Server service)
- Create a general exception in the Windows 2008 firewall for the following two executables
- Turn off the Windows 2008 firewall.
If the problem persists, please refer to KB #44239 respectively KB #1334
Windows 2008 Server with PXE Server service installed and running (firewall enabled)