RHEL 6 upgrade to RHEL 7 fails

Hi

I am trying to upgrade RHEL 6 server to RHEL 7. I ran preupg tool, fixed all failed items. Although some needs_action remained, but from my point of view these were not critical. After that I ran ~~~redhat-upgrade-tool --network 7.3 --instrepo https://example.com/pub/rhel7/~~~
After reboot system fails to boot with this message:

[!!!!!!] Failed to allocate manager object, freezing!

Do you have any idea what could be the problem here?