network installation on KVM fails to parse the kickstart profile

I'm trying to perform network installation to automate the deployment of KVM guests.

I'm able to use the following command line to install RHEL 7 guests without any problem. However, the same command line fails to parse the ks.cfg file when trying to install a RHEL 6 guest

virt-install \
-n myRHELVM1 \
--os-type=Linux \
--os-variant=rhel6 \
--ram=2048 \
--vcpus=2 \
--disk path=/var/lib/libvirt/images/disk1.qcow2 \
--graphics none \
--l http://x.x.x.x/rhel/6 \
--network bridge:br0
--extra-args "inst.ks=http://server/vm.ks.cfg"

In this case, the VM boots from the network but fails to proceed with the kickstart profile. Could someone help pls?