Having some problems with deploying a new OS from RIS.

The weird part is that it works, but yet don't work.

it works on physical hardware machines, but when I try to install a new OS in a VMware server setup it doesn't work. I have another setup where it works fine. The error on the virtuel setup is

after getting a DHCP-IP and waiting for a boot-file, it times out with this

pxe-e32: TFTP open timeout
pxe-e32: TFTP open timeout
pxe-e32: TFTP open timeout
pxe-M0F: exiting intel PXE ROM


In my opinion it should not be a HW-problem since this is virtual HW and it works on the other network.

Any idea what could be wrong.