The code uses the indicated variable inside the parfor loop as if it were a reduction variable, but other uses make it impossible for Code Analyzer to classify it. This happens, for example, when there are additional uses of the variable besides the reduction computation. This is invalid. Such uses imply an ordering in the parfor loop iterations, which is contrary to how parfor loops work.

Rewrite the application to avoid using the variable in the manner described in the explanation. For more information, see Reduction Variables.