If it happens one time, for a 2-ish week delay, I'd just let it go.
If you want to make it a little painful for them, demand a written explanation of exactly what happened, a calculation of any lost earnings, and compensation (perhaps via a rebate on fees) if the 401K provider was at fault. If your company payroll or HR was at fault, probably best not to take a giant dump on them (don't crap where you eat and all that...)