problem with VB code on some machines (.net bug may be)

I have made my first visual basic .net 2003 application and I get the
following message on 1 of my computers (it works on 3 others).

Mailer4u.exe - Common Language Runtime Debuggin Session
Application has generated an exception that could not be handled.
Process id=0x6b4 (1716), Thread id=0xc70 (3184).
Click OK to terminate the application
Click CANCEL to debug the application

I searched on google and found 1000's of people with the same problem for a
range of applications. Every one had different reasons and not one had a
working solution / fix. If any body has an idea can you let me know. If you
could also email me at d a v i d @ j e m d a m . c o m that would also help
(remove all the spaces from the email address first).

If someone would like to try my code on their computer and see if they can
repeat the problem you can download it here:

http://www.mailer4u.com

Thanks in advance for any one who can figure it out.

David