I would check the settings in gpedit.msc . Go to start - run and type "gpedit.msc" without the quotes. Then navigate to computer configuration - administrative templates - windows components - terminal services. First check the setting for 'limit number of connections' under the main folder, that may be set to '1'. Then check the setting for 'keep alive connections', that may be enabled. It should be set to disabled so that remote connections to your server don't stay alive longer than they need.

You might also check the setting for 'restrict terminal services users to a single remote session', but that setting is more for using the server as the client to connect to a different machine, not for controlling how many remote clients are connecting TO your server.

Next, go to the sessions subfolder. There check the settings for 'terminate session when time limits are reached' and 'sets a time limit for active but idle Terminal Services sessions'. These could be set at 'enabled' and some number of minutes respectively. These settings may also be influencing your inability to connect.

But if I had to guess, I would say the first setting I discussed is the culprit.

Good luck.