Tax problems: bio parents claimed foster child as dependent

2007 was my first year with a placement by the county DSS, so I am new at doing taxes with a dependent. My foster child lived with me for 8 months last year (IRS requires "more than 6 months"). When I tried to electronically file my taxes, my return was refused because my foster child had already been claimed as a dependent on another person's tax return (his parents, I presume). So, those of you more experienced that me: Are you claiming your foster children as dependents on your taxes? Have you ever run into this issue? How was it resolved. Thanks in advance for your advice and support.