May I use the statement "with" with Application.WorksheetFunction?

VBA for Exce doesn't like this part of code...
Other things go well...

With Application.WorksheetFunction
Test = Test + (Rng2(i) - Weibull(Rng1(i), ParA, ParB, TRUE)) ^ 2 / Weibull(Rng1(i), ParA,
ParB, TRUE)

Thanks, Alex.