FBA Not granting access to AD group users

In my FBA setting, individual user can be granted access to sharepoint site and works fine. It is able to resolve AD group but any user within that AD group is not able to get access to the sharepoint site. Same user when added directly gets access. Since these AD groups have more than 2000 users it is not possible to add them individually. Is there anyway of doing it? 

i followed this approach but it did not work.

http://social.technet.microsoft.com/Forums/office/en-US/9592df6b-d789-49c0-b1ec-142828cdadc8/fba-ldap-domain-group-members-getting-access-denied?forum=sharepointadminlegacy

sachin