A sequence local in a Sequence structure has not been assigned a value in any of the sequence frames. When this error occurs, the sequence local appears as a blank rectangle.
To correct this error, wire a data input to the sequence local in one of the sequence frames. Once the sequence local is wired, an arrow appears in the sequence local rectangle.
Alternatively, you can right-click the sequence local and select Remove from the shortcut menu to remove the sequence local.