Password change over VPN causes issues

Hello, I am a coop student working for a company that has off-site employees logging on to the domain over VPN on Windows XP. We are getting a lot of helpdesk requests from these users regarding password changes. When users attempt to manually change their passwords over VPN by pressing CTRL ALT DEL and going to the change password option they are able to enter their current password and new password. However, after they have clicked the "OK" button to accept the new password, they get an error message saying they could not connect to the Domain.

This is becoming a big problem, as many of the users are being locked out due to their passwords expiring, and a lot of work is being created for the the helpdesk employees. Any help you could provide would be very welcome. Even if you had some perspective on what exactly the issue is, I would be very grateful