Expenses for a failed adoption might qualify for the credit if followed by a successful adoption, but the two adoption efforts would be considered as one adoption and subject to the dollar limit per eligible child.
Adoption Tax Credit - How to Claim the Adoption Credit
Failed adoption attempts count, as long as its a domestic or special needs adoption. The credit is cumulative, however: if more than one adoption attempt doesnt succeed, or if you succeed after failing one or more times, your credit for all the attempts is limited to
$10,000 adoption credit has many strings - MSN Money