Adding values to user object attribute

I am using the code below to add a value to users' "employeeType"
attribute, 
but the "UserObject.SetInfo()" line always produces the error "A first
chance 
exception of type 'System.Runtime.InteropServices.COMException' occurred
in 
app.exe".

Can anyone tell me where I've went wrong?

Thanks,
Iain
 
        Dim UserObject As ActiveDs.IADs
        Dim strBuffer As String

        Try
            UserObject = GetObject(strDN)
            strBuffer = ""
            UserObject.Put(strBand, "employeeType")
            UserObject.SetInfo()
        Catch
            Msgbox "Error!"
        Finally
            UserObject = Nothing

        End Try