First, you need to check online that the restaurant accepts (for AAdvantage Dining purposes) the credit card you are using - in my home area, there are several local restaurants that accept AMEX, but do not include AMEX as an acceptable card to earn miles with (as indicated by lack of the AMEX logo in their details page.) This is most likely your problem, and it has been mentioned previously in the iDine Forum.
Secondly, since this is related to AAdvantage Dining by Rewards Network ('iDine,") this thread will be reolcated to the iDine Forum.