-

Error: The system event must contain at least one program instance.

In your project, a system event task is defined which does not yet contain a program instance.

The task configuration and the assignment of programs to a task is done using the 'Tasks and Events' editor.
  1. Double-click the error message to open the 'Tasks and Events' editor of the 'PLCnext' PLANT node. The suspected table line is marked.
  2. Assign at least one program to the system event by dragging the desired program POU from the COMPONENTS area onto the table line in the 'Tasks and Events' editor or by selecting the program from the 'Program Type' field.

Further Info
For further information on tasks and how to edit them refer to the topic "Task Configuration".