Ive never had any issues Efiling an amended return whether I did the original or not....why so many people struggle Im not sure. 

How I amend a return that I didnt prepare/file the original.

Create a return with exactly the same info as the original, have the EF box marked for the original return.
Save, give it a file name and Exit.
Now re-open the same file and activate the 1040X by checking the YEAR box at the top.
If a state return needs to be amended, open the state an activate their amended form.
Go back to the federal return and make the changes needed and type in your explanation on the 1040X.
Go to the Fed info Worksheet and mark the 2 boxes to EF an amended return.
Save and exit to the EFcenter.
You should see the Federal Amended Return in the list.
Highlight it and hit the EFNow button on the toolbar.