I'm willing to bet the problem isn't Outlook (I'm assuming we're talking
about Outlook and not OE), it's either your internet settings or, more
likely, the antivirus settings.
Control panel - Internet Options - Security - Custom. Then allow whatever
is being trapped.
But IMHO, the real problem is Norton. It's interpreting things you don't
think are problems as possible viruses. It's probably also set to
automatically prevent access rather than giving you the choice.
You have to decide on the balance between security and the ability to view
attachments that "could" have viruses (like .DOC and .XLS files). If you
want Norton protection, it can either warn you or automatically prevent
access. The initial default settings are very restrictive and prevent
legitimate attachments from getting through. You need to tweak the settings
to a point where you feel comfortable.