Hi Windy, and Technical,
I've just checked Outlook 2002 and Pegasus Mail, both are working fine on the new update for me (send and Receive with attachments).
Is it any particular kind of attachment you are trying to send (text, exe, image etc) I tested with a .gif with no problems. 
I'm trying .gif and .doc and could not send them.
Today morning I receive and send .doc files with easy...
In avast! iNews is said that a timeout problem related to SMTP communication was
fixed. Is this related to my problem? I think not because is not a timeout trouble... I´ll keep working but this new bug is really annoying... :'(