I have not created a scale image, and error code 518, "Scale image not loaded" appears in SMARTDAC+ GX/GP series. What should I do?

The scale image is turned ON under MENU key > [Screen change] tab > Settings > Settings menu [Display settings] > [Group settings]. Turn this OFF.
For details, see section 1.6, "Setting Display Conditions" in the user's manual.
User's Manual (IM 04L51B01-01EN)