Making SO Lines tab screen to FULL

When in a SO on the LINES tab a user try's to make the screen FULL and Sage throws out this error

 so_salesorder.m4l. [4045] error 65 Windows element does not exist or already exist.

When the user try's this in another company she doesn't receive the error and when she logs in with another user account and try's she doesn't receive the error either.