Unable to insert a line within a box

What causes this issue?

You chose the function "Insert line".
The cursor points to a line containing a frame link or cut by a frame
link.

System Response

The system cannot execute this function in this line.

How to fix this error?

If you want to insert a line feed here, you must first expand the
frame. If you only want to change the position of individual screen
elements, use the functions "Move" or "Move area".

Error message extract from SAP system. Copyright SAP SE.