My tax return was rejected due to my dependents already being claimed, my ex-boyfriend has claimed them. This is 2 years in a row that he has has put them down on his tax return. He is not the custodial parent and he only sees them when it is convenient for him. No child support of any nature. What can I do?

Report him to the IRS for fraud

Wow, your ex has not manners. He should be reported immediately. Also, report him for not paying child support. Get an attorney.

My tax return was rejected due to my dependents already being claimed, my ex-boyfriend has claimed them. This is 2 years in a row that he has has put them down on his tax return. He is not the custodial parent and he only sees them when it is convenient for him. No child support of any nature. What can I do?
The same thing happened to a friend of mines. She had to file a paper return and then prove she has the right to claim her kids (that live with her and has not seen their father in over 3 years or received monies for for them) It is a long process but you will win in the end. Also you can file a amened return for up to the last three years if this problem was going on then.

Thanks guys, I think I am just more frustrated than anything..

According to Pub 501, since you and your ex are both parents and not living together, if both claim the child as a dependent then the one who "wins" is the one with whom the child lived longer during the tax year. That sounds like you. You should contact the IRS and insist that you are the rightful one to claim the deduction.

http://www.irs.gov/pub/irs-pdf/p501.pdf