The problem is that TurboTax is assessing a penalty as if I contributed too much based on the limits for a Roth IRA, not a 401(k)
Back up...Are you also entering Roth IRA contributions in the section for IRA's along with having Roth 401(k) deferrals on the W-2?
What penalty is the program saying you will have?
sallydyer57, somehow you've mistakenly entered this under Deductions & Credits -> Retirement and Investments -> Traditional and Roth IRA Contributions. Go back and remove the entry you made there. It is not a Roth IRA contribution.