If your child is totally and permanently disabled, her age does not matter, she can still be considered a qualifying child if she lives with you for more than 6 months of the year and meets the rest of the criteria to be a qualifying child.
As a qualifying child, they cannot provide more than half of their own support. The parents do not have to provide more than half of her support, she just cannot provide more than half of it. Support includes, food, housing, insurance, transportation, medical needs, etc. Here is a worksheet to determine if she does provided more than half of her own support. If you did not claim her in previous years, it is possible that you could go back and amend your return if she otherwise qualifies as your dependent.
The following criteria must be met to claim someone as a qualifying child:
If she did qualify as a dependent in previous years and you did not claim her, you can go back and Amend Your Returns for the past 3 years to claim her as a dependent.
If she DOES provide more than half of her support, then you would need to go back through the answers on your return and double check your answers. If she is not able to be claimed as a dependent, then it is best to delete her from your return.
Thank you for your reply! I finally found out why I was stuck. There was an option I did not check, "Paid for more than half of their living expenses and other support ". That explained why I did not have problems in previous years. Your input that the dependent can't support herself more than half was useful. I'll keep this in mind for the next year and will talk to a tax adviser. Thanks again and have a good one! Akatsnel.