Error "Fill in all required entry fields": In our own transaction ZOPE I have added a pushbutton which invokes an InputScript. The first action is F17, so my InputScript starts with

Screen ZMT_PP_OPERATION.1000
Enter "/17"

But this results in an error message "Fill in all required entry fields" which doesn't occur when I press F17 manually in this screen. What could be the reason?

Use

Enter  "/17"

without the preceding
Screen ZMT_PP_OPERATION.1000

When you start the InputScript with a "Screen" command, GuiXT first presses "Enter" and then continues the processing when the next screen is displayed. "Enter" results in the error message "Fill in all required fields" whereas the immediate F17 corresponds to what you are doing manually.