Error Message 451

Hi,  please help.

 

Windows XP,  Norton AntiVirus 2011, MS Outlook.

 

For several days now the following occurs:

 

As soon as we have clicked the send button for an email the following Norton error message appears:

 

"451 Temporary local problem - please try later"  followed by the sent "From" and "To" information.

 

I have tried the following to overcome this problem:

 

1) uninstalled and then reinstalled Norton AntiVirus 2011;

2) full scan;

 

I now have to temporarily (for 15 min) disable Norton's Email Protection so that I can send an email - which is obviously only a very temporary solution.

 

What can I do solve this problem??  Please help