I'm a little confused as to what password you are trying to change. Is it the local account to access the T610 or the AD account used for the RDP connection? To access the T610 do you use a local account or an AD account?
If it is the AD account you are trying change, I think that the issue is VPN related and would concentrate on the domain controller. Perhaps it does not recognize the sub-net and is therefore refusing to relay the DHCP information over the VPN. Does the event log show any blocked connections?
If you are using an AD account to log on locally and then launching freerdp, I would suggest using a local account that does not change and auto-launching freerdp so that the user never has to put in local credentials (or even see the local OS).