If you are capturing to the core server then your PXE rep doesn't need to be a Preferred Server.
You should double-check that the account you're using to access the capture share has write/modify rights and not just read only rights.
I am using LDMS 9.5, but I attached the XML of my Win7 x64 capture template. It's pretty basic, just a capture using ImageW V2 (like you) and storing it on the preferred server on my subnet before rebooting the client.