Trouble replying to e-mail messages

I am using Outlook 2003 SP3 and just installed Norton Internet Security 2010 ver 17.7.0.12.  Since installing I can send and receive e-mails but cannot reply.  When I create a new e-mail it is placed in my outbox and is sent without problem.  When I hit reply to (or forward) an existing e-mail, the e-mail remains in my outbox indefinitely.

 

Any ideas?