Can´t select correct axis in background image

Hello, when I want to add a background image, one of the axes isn´t still accepted. F.E. - I have table with columns X, Y, Z. All the columns have the same type (I also tried the same values) and are recognized in column mapping as X axis = column X, Y axis = column Y .... So the scatter is OK. But when I try to add the background image, only column X is "correct". Screens in attachement. If choose column "Y", it won't allow me to map it.

Thank you M.