The return I filed today on TurboTax was rejected by the IRS because it was seen as a duplicate. My original 1040, which I did through the new IRS portal was rejected.

[mejanka]

I sent in a 1040X through the mail, but got a letter from the IRS saying "we are unable ot read the 1040X." So, I submitted via TurboTax today, but I've gotten a rejection because "the Primary taxpayer's identification number assigned to this return has already been filed. How do I resolve this?

[xmasbaby0]

It is not clear what all you have done--or are trying to do.   If your original Form 1040 was rejected, then you have not filed a tax return.  You do not "amend" a rejected tax return.  Amending --using a 1040X -- is only done if you have already filed a tax return and it has been processed by the IRS, and then you realize you need to add information or correct something.  Amending is not the process for fixing a rejected return.    

If your original Form 1040 was rejected when you tried to e-file it, then you can file it by mail instead---print it, sign and date it in ink, and mail it in.   

But...first....please explain in detail---and in sequential order----what you have done.