Step 1. Login to your windows server
Step 2. Launch the Registry Editor in Windows Server, go to Start and then Run. Type regedit in run menu and hit enter. To launch Registry Editor in Windows Server 2012 R2, press Windows key + R. Type regedit in run menu and hit enter.
Step 3. Once Registry Editor window is launched, navigate to HKEY_LOCAL_MACHINE\System\CurrentControlSet\Control\TerminalServer.
Step 4. By selecting the Terminal Server registry, you would see the registry key fSingleSessionPerUser on the right panel.
Step 5. Right-click on fSingleSessionPerUser key and then click on Modify.
Step 6. Change the key value from 1 to 0 as shown in the screenshot below, and close the Registry Editor. The value 1 denotes single session for each remote desktop user, and 0 denotes multiple sessions for each user.
Multiple RDP sessions for the single user enabled.
If fSingleSessionPerUser key is not available then you will need to create it manually. To add a new key, click on Terminal Server >> New >> New DWORD (32) Value. Name this key as fSingleSessionPerUser, set its value to 0 and close the Registry Editor.