Simplified (Tested Successfully)
Note: Use Google to find the file.
termsrv.dll – 215,552 bytes
5.1.2600.2055 (xpsp_sp2_beta1.031215-1745)
Backup original termsrv.dll by renaming c:\windows\system32\dllcache\termsrv.dll to termsrv.dll.bak
Copy termsrv.dll to c:\windows\system32\dllcache
Copy termsrv.dll to c:\windows\system32\
Open Windows Registry Editor Version 5.00 and add the following dword values:
Windows Registry Editor Version 5.00 [HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Terminal Server\Licensing Core] "EnableConcurrentSessions"=dword:00000001 [HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows NT\Terminal Services] "MaxInstanceCount"=dword:00000002
Note: MaxInstanceCount can be adjusted to fit individual requirements.
Reboot