Turbo tax is combining both mine and my husbands 401k contributions together as one sum and we are now receiving an error that we have an overpayment.

[Vanessa A]

If the amounts for your contribution are being combined, this is likely due to not selecting the person who it belonged to.   You will need to go back and check the owners of the W-2's.  If you each have a W-2 with code D or AA in box 14, and you did not choose that one W-2 belonged to you and the other belonged to your husband, then this would create this error.

To fix this, simply go back to the W-2 section and select his name for his W-2 and your name for your W-2.  By default when you enter a new W-2, the primary tax payer is selected, so if you do not answer that question, it goes to the wrong person. It is easy to click through that spot.

If this does not work, you can delete both W-2's and re-enter them paying special attention to who's name they are listed under. 

[Opus 17]

The error you describe could also be caused by entering your retirement in the IRA section.

Don't enter your 401k in the IRA section.  A 401k is not an IRA, it is only reported on your W-2 and is captured automatically by Turbotax.  The IRA section is only used for actual IRAs that you privately open at a bank or broker that is separate from any workplace plan.