Would it be possible for you to perform a test with any of the other instances of CDOSYS? If you can please try using one of your other CDOSYS based scripts to send an email to the same individual and also use the same settings. Using the same settings and email address are important to help exclude these values as a possible source of the problem.
This will help to indicate where the problem may be, if you are successful with the same settings and details but in a different script on the same server then it would indicate a problem with this specific implementation. Otherwise it would indicate a problem with the object or settings. Please give this a try and let us know what you discover.