Visible length is shorter than defined length (not transformed)

What causes this issue?

You are editing an input/output field for which the "scrollable"
attribute is set, and want to change it into a box. The visible length
of the screen element is less than the defined length.

System Response

You cannot scroll in a box text. The system therefore cannot convert
the output field into a box with variable text if the visible and
defined lengths differ.

How to fix this error?

Before converting the field, remove the "scrollable" attribute. You can
do this in the "attributes" screen or in the element list.

Error message extract from SAP system. Copyright SAP SE.