Can't accept new action goals. Controller is not running [closed]

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Sometimes after running the robotic arm for a while, the arm controller stops to accept new action goals and then we see this error message on the universal_robots_ros_driver node ("Can't accept new action goals. Controller is not running"). We resolve this problem simply by killing and relaunching the universal_robots_ros_driver node and everything works fine after that. What is really the problem here? Why does it stop accepting new action goals after some time of running the the controller, the ros driver, and the arm? Can someone help solve this problem without having to relaunch the ros driver script?