Recently I found that on my VPS server there is incorrect time often called time drift. As you know having correct time is very important - especially in Active Directory environments. Back to my case - I have VPS running on XEN and I reported to hosting company this issue. They replied that they will not change ntp settings for hosts but they said that I can do it by myself.
So encouraged by them (of course by not solving my ticket at all) I did small digging and I found this solution.