LabVIEW can recognize and parallelize simple reductions, in which one value is computed from a series of values. This error occurs because the iterations of a For Loop configured for parallel execution might depend on each other through shift registers and the computation is not a recognized reduction.
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.
Refer to the Parallel For Loop Reduction VI in the labview\examples\Structures\Parallel For Loop directory for an example of using a For Loop with parallel iterations.