The problem is .AddAttachment()
is a method not a property try changing your code like this;
Call .AddAttachment("c:\users\samplb\logoblack.gif")
or to return the attachment as a CDO.BodyPart
use;
Set cdoBodyPart = .AddAttachment("c:\users\samplb\logoblack.gif")
Note: See the AddAttachment Method (MSDN Library) for more information about the method and how to use it.