If when you go to E-file a return that was previously accepted as an extension and the E-file button is grey or diagnostics says it was already filed, make sure the extension option on the main information page is not marked any longer. The section where you can check this says: What form(s) are you e-filing using PINs?
The option to E-file the return should be checked now instead. Also, on the 4868 un-check the checkbox next to where it says check here if using this form or delete the form from the return.
You can now e-file the return.
This information applies to all years of UltimateTax software.