"User Must Change Password At Next Logon" is a flag that indicates that a temporary password has been set by someone else (usually an admin), and that to maintain account security the user is forced to change the password at next logon.
Are you sure that you changed this on the Admin account, or on a service account, such as Network Service? Because you do not want to set this for service accounts. (If the Admin account is being used as a service account, changing the password can potentially break things.)
To solve the issue quickly, I would recommend calling the company that you rented the VPC from, asking them to reload the base image onto your virtual machine. Then, once you get back into the virtual machine, I'd recommend that you go into Admin Tools: Users and Computers and create a new user account for yourself. That way you don't use the Administrator account, and aren't tempted to change the password and potentially break any network services that were set up to use that account as a service account (a bad practice, but it does happen.)