CreateObject returns an object which must be assigned to a variable. Try the following modifications (in bold):

<B>LOCAL oMAPI</B>
SET CLASSLIB TO MAPIMail ADDITIVE
<B>oMAPI = </B>CREATEOBJECT("cusMAPI")
<B>oMAPI</B>.SendMail("","","CHUCK HENRY","Change Order Test","Testing Body Text","ChgOrder.txt","","")

The error you are getting is because cusMAPI is a class, not an object. CreateObject creates an object based on the class given in parameter.