ID:235002 External text editor can be used only after you close all the opened text files in the Quartus Prime Text Editor window

CAUSE: You tried to use an external text editor. However, there are opened text files in the Quartus Prime Text Editor window. You cannot use the external text editor unless you close all the opened text files in the Quartus Prime Text Editor window.

ACTION: Click OK to close the message dialog box. Close all the opened text files in the Quartus Prime Text Editor windows.