Adding windows user group to NAV and assign roles

Dear All,

May be this is one of the simplest queries.

I am trying to add a windows active directory user group (security) into Dynamics NAV and assign roles. I have around 65 users in total from which only 15 will have super user privileges and other elevated privileges. We have created a customised role called "ERPUSER" for the normal users. I have created a user group (security) in my Active Directory called "ERP_Users" and have added all normal users into this group. When I added this group alone into Tools --> Security --> 'Windows Login' in NAV, I am able to synchronize without any error. When the users tries to login, they can see the database in the DB list using windows authentication but cannot login with the error "Invalid User Name / Password". I read somewhere that I can use user groups only to assign roles to the users and need to add individual users into dynamics NAV. I added some of these users along with the user group, gave no roles to the users directly but gave the user group "ERPUSER" role. When I tried to synchronise I get the error:

** Error ***
The following SQL error or errors occured:

15151,"42000",[Microsoft][ODBC SQL Driver] Cannot find the user
'$ndo$ar$000.......', because it does not exist or you dont have permission

SQL:
GRANT SELECT, INSERT, UPDATE, DELETE on "Object" TO [$ndo$ar$000.....]
*** Error End ****

I am not sure what I am doing wrong. All I am trying to do is to avoid adding all the users into NAV and assign role and instead create an AD user group and assign roles to that. I am not sure how this is achieved, or whether this is possible.

Any help is appreciated.

(I read in one of the post about a document 'Security Synchronization in NAV.doc', but unable to find the doc anywhere in partnersource or otherwise)

Regards

Najja