You have connected two strictly typed VI refnums whose connector patterns do not match.
In this example, the strictly typed VI Refnum on the front panel does not match the connector pattern the Call By Reference Node expects. However, because the Call By Reference node is already wired, it cannot adapt to the type of the refnum on the front panel.
To correct this error, change the connector pattern of the front panel VI Refnum to match the Call By Reference node. To select from patterns you have previously used as strict types, right-click the front panel refnum and select Select VI Server Class»Strictly Typed VIs from the shortcut menu and select a pattern.
To select the connector pattern of a saved VI, right-click the front panel refnum and select Select VI Server Class»Browse from the shortcut menu. When the patterns of the two refnums match exactly, the wire appears as a solid wire.
In the example above, you could remove the wires from the Call By Reference node and allow it to adapt to the connector pattern of the refnum control.