Can't send email from Excel or Word or Powerpoint

[Penguin]

Hi there
For some reason, I can no longer send emails using the send command in any
of Word, XL or PPT. I get error messages in each which are slightly
different but which are:

WORD - Logon failed. You must log on to Microsoft Exchange to access your
address book. Error code: "Unspecified error".

EXCEL - General mail failure. Quit Microsoft Excel, restart the mail system
and try again.

PPT - There was a general failure with the email system and this action
could not be completed.

Windows Live Mail is set as my default email programme and in each case is
opens when I choose 'send' but all I get are the above error messages.

Any help will be gratefully received.
Thanks