I have integrated UR5 with siemens PLC S71200 . I can able to trigger Protective Stop while in Manual mode but not in Auto mode . pls provide solution on this.
You’re able to unlock protective stop in manual mode? That sounds like a bug. 
For it to work in Automatic Mode, you have to be in Remote Mode and not just Automatic Mode. Remote Mode allows for remote starting and stopping the robot.
You can enable it by going to the settings in the upper right corner and enabling Remote Control. Then you can select Remote Mode when in Automatic Mode.