In this situation, you have 2 options:
Click YES to the message above. The drawing will then open for you to edit. IMPORTANT: This will open a copy of the drawing, not the master drawing, so any changes you make will be separate from the master drawing. You will also need to save the drawing with a different name.
Click NO to the above message and then delete the .EFL file, you will then be able to open the drawing. IMPORTANT: Please check that another person really is not amending the drawing before deleting this file.
If the above instructions are not working it may be that the .EFL file is being synchronised with a Cloud based system or something similar, in which case the automatically deleted .EFL file gets put back by the synchronisation process causing the issue to remain. To get around this you will need to set your synchronisation system to ignore .EFL files.