[02/03] Ambiguous Error

i'm getting following error while getting data from sql server 200 in drop down lists.

Specified argument was out of the range of valid values. Parameter name: adm02
here adm02 is the groupId.

VB Code:

'Display current user data when user ID is not 0
            If UserId <> 0 Then
                Dim objUser As BusinessLogicLayer.Users = Users.GetUserById(UserId)
                intId.Text = Convert.ToString(objUser.Id)
                intId.Enabled = False
                txtUsername.Text = objUser.Username
                dropRoles.SelectedValue = objUser.GroupId  [B]'in this line error comes; value is taken correctly that's "adm02"              [/B] 
 
                dropBranch.SelectedValue = objUser.BranchId
 
                If String.Compare(User.Identity.Name, objUser.Username, True) = 0 Then
                    IsCurrentUser = True
 
                End If

can u help in resolving this error??