For Loops can run in parallel only when LabVIEW can determine that loop iterations do not depend on data from other loop iterations. If an array is passed through shift registers, each loop iteration must read or write to disjoint elements of the array. This error occurs when a For Loop is configured for parallel execution and more than one iteration of the For Loop might access the same array element and at least one might write to the element.
To correct this error, remove the dependence between loop iterations or disable parallelism on the For Loop. To disable parallelism on the For Loop, right-click the For Loop, select Configure Iteration Parallelism from the shortcut menu, and remove the checkmark from the Enable loop iteration parallelism checkbox in the For Loop Iteration Parallelism dialog box.