Once you Recreate PXE Boot Image it takes a while for them to recreate on all PXE Servers, use the Status button to check they've finished updating.
If you download the DS Samples, there's a script to run on the PXE servers to set the startup order of the PXE services:
http://www.symantec.com/docs/HOWTO4439
But how you proceed will depend on if the problem is model specific or not.