This error is usually received when the client booting up via PXE is having difficulty communicating with the DHCP/PXE server. The common troubleshooting steps and/or causes of this problem are as follows:

1-The PXE client is connected to a managed switch that does not have portfast enabled and/or is running spanning-tree. Portfast will need to be enabled. To read more about what spanning-tree and portfast are, see article 3096, "What is Spanning Tree? What is PortFast?"
2-The DHCP/PXE servers reside on a different subnet than the PXE client. IP helpers need to be in place. See article 1331, "Configuring PXE to work across VLANs."
3-Check the DHCP server and verify that the DHCP scope has free IP addresses to lease out (make sure they are not all used up).
4-If the above steps do not correct the issue, place the DHCP Server, PXE server and a client computer on a hub. Test PXE to see if the same message is received. If the same error message is not received, this is a good indication that there is some factor on the network not permitting the DHCP/PXE protocols to be passed down to the client computer.
Place a hub between the PXE client and the switch the client is connecting to. If at this point the PXE client works successfully, please review step 1 of this article.
5-Use TCPView to verify the DHCP ports 67 and 68 (http://www.microsoft.com/technet/sysinternals/utilities/TcpView.mspx). MTFTP Port 69 are showing.
6-If this problem is still occurring after testing out the above, collect sniffer traces from the DHCP/PXE server(s) and contact Altiris Support Services.
7-If DHCP server is on the same box as PXE server follow the option to enable 060 scope option. Article ID: 17347 Creating and setting option 060 on a DHCP server
8-The NIC could be disabled on the Client machine.