I invested 2,000 into my IRA and deducted it from my 2010 Federal Taxes, but I failed to date the check and it was returned to me but AFTER the April 15th deadline. So now I'm filing a 1040x form and need to know how I should word my explanation of my error? Also do I need to send in a copy of my 1040 form with it?

“So now I'm filing a 1040x form and need to know how I should word my explanation of my error?”---->You should file an amended tax return if you need to correct any piece of information that will alter your tax calculations. You can briefly explain the reason why you are filing your 1040X on 1040X part3.
“ Also do I need to send in a copy of my 1040 form with it?”--> In order to properly amend your tax return, you actually have to file two returns. You file a new IRS Form 1040 and an IRS Form 1040X. You have to attach all the schedules and documentation to the Form 1040 that you did the first time you filed it. The Form 1040X has to be filed on a paper return; amended tax returns have to be mailed to the IRS on paper for manual processing. The IRS typically processes an amended return about 8 to 12 weeks, but this process can take longer during the IRS's busiest times. Be aware that you have three years to make any corrections that result in additional tax refunds( if you are subject to tax refund).Your state tax liability may be affected by a change made on your federal return. For information on how to correct your state tax return, contact your state tax agency.