To enable concurrent remote desktop session, Go to

• Open Control Panel & Open Administrative Tools
• Go to Services
• Choose Remote Desktop Session then Right Click & Stop the Services.

• Goto c:\windows\system32  & copy termsrv.dll and paste it in the same folder. It automatically paste the copy of termsrv.dll.
• Right click termsrsv.dll -> security -> system ->advance-> change-> administrators. Now administrator user get full access to change/modify termsrv.dll file in system32 folder.

• Download  termsrv.dll file from link below 

      For Windows 8 :   windows8-termsrv.dll.zip

     For Windows 8.1 : windows8.1-termsrv.dll.zip

• Rename termsrv,dll file  (32 bit/64 bit) and replace file in system32 folder.

• Again goto control panel–>administrative tools –> services –>remote desktop services and start this service.

• Reboot & Enjoy, Now concurrent users use RDP 😉