Hi, I'm David McRae, a CPA at Form 990 Help Calm. I have prepared a list of 12 of the most common errors made on Form 990 and 990 EC. These twelve items, some of them, can result in the return being deemed incomplete, which can subject the organization to late filing penalties. So here we go: 1. Filing on the wrong year's form: If you have a fiscal year organization and the year begins in, let's say, 2011 and ends in 2012, which year's form do you use? Well, it would be a 2011 Form 990 because the beginning of the year controls. 2. Failure to prepare and attach Schedule A: Schedule A is the public support calculation and it's required for all 501 C 3 organizations. If you don't have it, your return is incomplete. 3. Failure to indicate on Schedule A why the organization is not a private foundation: This is a simple check. Make sure you don't miss it. 4. Failure to attach Schedule B: Schedule B is your list of large donors, generally meaning donors who give at least $5,000 during the year to the organization. Be sure to read the instructions to see if it applies to you. If it doesn't apply, be sure to check the that says you don't have to file it. If you fail to check this, the IRS will be looking for that Schedule B and you will receive communication. 5. Failure to attach Schedule O: Schedule O is mandatory for the full Form 990 and is mandatory in certain cases for 990-EZ. My recommendation is that you always file a Schedule O with your return. 6. Balance sheet net assets do not equal net assets on page one above the return: Those two things have to agree. If you have professional tax software, you'll...