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This tutorial contains instructions to fix the error “To sign in remotely, you need the right to sign in through Remote Desktop Services”, when trying to connect from Windows Remote Desktop (RDP) Client machines on a Windows Server 2016 which is running Remote Desktop Services.
Problem: Remote Desktop Client users cannot connect remotely (through RDP) to Terminal Server 2016 and receive the error: “To sign in remotely, you need the right to sign in through Remote Desktop Services. By default members of the Administrators group have this right. If the group you're in does not have the right, or if the right has been removed from the Administrators group, you need to be granted the right manually.”
To resolve the “To sign in remotely, you need the right to sign in through Remote Desktop Services” apply the following actions on Remote Desktop Services (RDS) Server 2016 :
<fc #ff0000>Step 1. Add Remote Desktop Users to the Remote Desktop Users Group.</fc>
<fc #ff0000> Step 2. Allow the log on through remote desktop Services. </fc>
<fc #6495ed>Win</fc> + <fc #6495ed>R</fc> keys to open run command box.
<fc #6495ed>Computer Configuration→ Windows Settings→ Security Settings→ Local Policies→ User Rights Assignment.</fc>
Notes:
1. If you still have sign in problems then restart the RDS server or just open command prompt as administrator and type the following command to apply the new group policy settings (without restart) :
gpupdate /force
2. If after updating the Group Policy settings, the problem is not resolved, apply the following modification at Group Policy Editor: