Get manager out of LDAP

I am fairly new to InfoPath.

Using Visual Studio 2005, I am able to get name, title, location, department, and phone number out of LDAP. I am trying to get the current user’s manager, but am having trouble getting it.

I am using the following code from Microsoft:

Dim ManagerName As String = personnel.Properties( “manager”).Value.ToString()
ManagerName = ManagerName.Substring(3, ManagerName.IndexOf(“,”) – 3)

I get the following exception:
NullReferenceException was unhandled by user code.
Object reference not set to an instance of an object.

Please help. Thanks