The solid line indicates that the Front Panel object is locked. When any item is locked, it cannot be moved or deleted and no properties of the object can be modified. Additionally, the object will be not be selected by clicking on it and will require a click and drag selection.
To rectify this, select the object such that it is highlighted and then click on the Reorder button on the LabVIEW toolbar. From the drop-down menu, select Unlock.