I used IRS form 1040X to add my dependent grandchild to my 2013 tax year. The form was not any problem to complete. My question is what supporting documents, forms or a whole return (original or as modified by applying the 1040X entries.I wrote out the line number adjustments for the individual form lines. Completed the exemption section showing that I add a dependent and the change in count. Since adding the dependent changes EIC, Child Tax Credits, and taxable income. The full modified tax return should be attached? Or just the main forms?What should I include to support my right to claim this new dependent on to my taxes? I need added support due to the original problem where my electronic federal filing rejected Due To The Dependent's SSN was already used on another return. I know who filed using my grandchild as there dependent, which is not valid!And one had any experience with similar matters?Thanks for any and all help posted.

When two people claim the same child as a dependent, the system will flag the returns and not allow you to file electronically. File by mailing in your return. The IRS will look into the matter and, no doubt, contact you to supply the needed documentation.

AK has it right. Submit your case to the IRS and let them sort it out.

As for forms to file with the 1040X- include any forms that are different from the forms of your original filing, or are new (i.e. were not part of your original filing).