After a period of inactivity, the UI loses connection to the CP and the following window appears:
<Please see attached file for image>
To resolve the issue I added the following line to the uc4config.xml:
Time in minutes in which the UserInterface sends messages to the Automation Engine in order to keep the connection.
This parameter does not depend on <tcpip_keepalive>. The setting <tpcip_keepalive> activates and keeps the connection on socket level which means that the time interval of keep-alive packages cannot be influenced. <active_keepalive> addresses the program level.
So now the uc4config.xml looks like:
<!--browser type="Mozilla Firefox">/users/uc4/firefox/firefox</browser-->
<trace count="10" ra="0" tcp="0" xml="0">../temp/UCDJ_TRC_##.TXT</trace>