Currently we are trying to connect LDAP on Dot Net Nuke 7, Unfortunately, Access To Global Catalog is always FAIL.

We have also tried Inputting on Root Domain

DC=DomainName,DC=com
DC=DomainName,DC=local
For this one error is object not set to reference.

We have also read some forum about this kind of issue but we failed to get the right answer.

http://www.dnnsoftware.com/forums/forumid/89/threadid/228293/scope/posts

BTW, Sophos is installed in our Server, But we have checked already and LDAP/Active Directory is already enabled in it.

http://esa.sophos.com/docs/wsa/swa_docs/ws1000/tasks/ConfigSysActiveDirectoryAccess.html

We have also verified whether our Global Catalog is working already through this link technet.microsoft.com/en-us/library/cc756476%28v=ws.10%29.aspx and verification is successfully so our Global Catalog is working correctly. We have also tried to follow the instruction in the link below but we still encounter Global Catalog FAIL http://kishanzunjare.blogspot.sg/2011/04/setting-up-dotnetnuke-dnn-to-work-with.html