Your network consists of a single Active Directory domain. All servers run Windows Server 2003 Service Pack 2 (SP2). All client computers run Windows XP Professional Service Pack 3 (SP3). You deploy a server named Server1 and install Terminal Server. After four months, users report that they can connect to Server1 by using Remote Desktop Connection, but are unable to log on. You verify that the user permissions have not changed. You need to ensure that users can log on to Server1 by using Remote Desktop Connection. What should you do? （）

A. Restart Server1.
B. Restore the system state of Server1.
C. Install and configure Terminal Server Licensing.
D. Modify the Terminal Services service account on Server1.