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Avoid creating cycles on the block diagram when you create a subVI from a selection. Cycles occur if a data flow originates from an output of the subVI and terminates as an input of the subVI.

Identifying cycles while making selections is difficult, but LabVIEW detects them. If LabVIEW detects a cycle, it displays a dialog box describing why it cannot create a subVI. However, you can copy the selection into a new, separate VI.