This error message may be suggesting that you've not only entered the $19,000 as a 401(k) elective deferral but have also entered some amount as a Roth 401(k) contribution. When that's the case, TurboTax flags the elective deferral as exceeding $19,000 when it's actually the sum of the elective deferral and the Roth contribution that exceeds $19,000.
