can't start kdump service on virtual machine

# service kdump start
No kdump initial ramdisk found.                            [WARNING]
Rebuilding /boot/initrd-2.6.32-504.23.4.el6.x86_64kdump.img
No module vmmemctl found for kernel 2.6.32-504.23.4.el6.x86_64, aborting.
Failed to run mkdumprd
# lsmod | grep vmmemctl
vmmemctl        13966 0

Fixing VMMEMCTL module issue:

You can disable this module by editing  /etc/vmware-tools/locations and changing answer VMMEMCTL_CONFED from yes to no.

More general approach:

More general way to handle missing modules is to ignore the ones which can not be found:
Edit /etc/sysconfig/kdump and set MKDUMPRD_ARGS="--allow-missing"
# service kdump start
WARNING: No module vmmemctl found for kernel 2.6.32-504.23.4.el6.x86_64, continuing anyway