Icon assigned to element & (cannot transform to graphical element)

What causes this issue?

You are editing a text field on the screen to which an icon is assigned
and want to convert it to a graphical element.
Not all types of graphical elements accept icons. Boxes cannot have
icons.

System Response

Conversion rejected.

How to fix this error?

If you want to convert the text field to a box, you must first delete
the assignment of the icon to the text field. You can do this in the
"Attributes" screen, or in the field list by overwriting the icon name
with blanks or cancelling it with '!'.

Error message extract from SAP system. Copyright SAP SE.