Exchange 2K Whopper!

Here is the deal: I have ONE client who's name cannot be resolved to the mail server. I have deleted and recreated her account. She is on the network ( can ping and access other shares),her account in AD looks like everyone elses, however, when Itry to add her to the Exchange server, I get the name cannot be resolved. I have never encoutered this and it has really hung me up!! Any suggestions???