リモートデスクトップをConcurrent状態にした場合に、同じユーザーが複数のセッションを使えないようにする

Start Registry Editor (by default, this is located at c:\windows\regedit.exe).

Go to the following registry key:

HKEY_LOCAL_MACHINE\
System\CurrentControlSet\Control\TerminalServer
If the fSingleSessionPerUser value doesn't exist, create a new DWORD value named fSingleSessionPerUser
Open the fSingleSessionPerUser value. The possible values for this setting are as follows:

0x0
Allow multiple sessions per user
0x1
Force each user to a single session

Enter the new setting, and then click OK.