Cobbler ERROR, 2nd router? - "PXE-E51: No DHCP or proxyDHCP.."

Dear All: Have you seen this ERROR before? ------ PXE-E51: No DHCP or proxyDHCP offers were received ------ That's what I see at the server where I want to install CentOS onto (via KVM). I made sure the Cobbler script is working, tested the install on another server where the install worked. I found this list of possible causes for such an error: ------ * DHCP services are not available on the network to which the PXE-enabled NIC is connected. * A DHCP proxy or IP helper address is not configured for the subnet on which the PXE client is connected. * The switch port connected to the PXE NIC is running Spanning Tree Protocol, EtherChannel Protocol, or Port Aggregation Protocol and is thus not activated immediately when a link is detected. This forces the DHCP request from the PXE client to timeout. * DHCP is available on the network, but PXE is not. * The network cable is not attached to the PXE-enabled NIC on the target server. http://h18000.www1.hp.com/products/servers/management/rdp/knowledgebase/0... ------ I can ping and access the server that I want to install to ... so all is fine with cables, and that is on the same networks, same subnet. I also double-checked the IP and MAC address, all correct. Now I wonder if maybe there is an issue because of the HP switch that server is connected to. We have two 24-port HP switches stacked up -- that is, this server is connected to the 2nd switch which is connected to the first switch. Could that be a cause? Another possibility: Presently the server where CentOS should be installed has "Proxmox VE" as an OS running, that's a virtualization system for VPS. Could it be that this somehow overwrites the Cobbler "offer"? Any suggestion is welcome. Best, Frank