I found this specific to California, and now I'm totally confused. (Mondays am I right?!) Wait - is it Monday?
One last find then I'm out. From the Help ↓
No, the IRS does not currently allow e-filing of Form 1040X. Per the Amended Return FAQs,
At this time, the Form 1040X, Amended U.S. Individual Income Tax Return, is not accepted electronically; only an original tax return may be electronically filed. You must file a paper Form 1040X. If you are due a refund, you will be issued a check and cannot use direct deposit.
However, the E-file Amended Return Wizard has been activated in the Individual Module because you can e-file an Amended Form 114. See Individual E-file Amended Return Wizard Note Prior to E-filing a Federal Form 114 Amended Return for more information.