Please follow the steps to enable multiple remote connections on windows server 2012:
1. Login to the windows server 2012 via. RDP
2. Open command prompt. Type gpedit.msc and open Local Group Policy Editor.
3. Go to computer configuration –> Administrative Tempalates –> Wondows Components –> Remote Desktop services –> Remote Desktop Session Host –> Connections.
4. Search for “Restrict Remote Desktop Services users to a single Remote Desktop Services session”
5. Right click on it and click Edit.
6. Select the option of “Disabled”, apply and click Ok.
7. Go to the command prompt and type “gpupate” and enter.
It will update the policy and result will be as follows:
Computer Policy update has completed successfully.
User Policy update has completed successfully.
User Policy update has completed successfully.