Are the machines you are trying to provision joined to your domain? I have seen the get core version response error when my systems is not joined to the domain.
Try the following to resolve your issue:
Manually unprovision your system through the ME.
Verify that the machines are joined to the domain.
Delete all references to your systems in Altiris.
Restart your remote system provisioning process.
yes the machines are joined to the domain, users are actually using the systems.