Since you didn't give us the error message, see if one of these applies.

Courtesy of Michael Santovec:
http://pages.prodigy.net/michael_santovec/techhelp.htm

Err Msg: The Message Could Not Be Sent. Some recipients not valid
(Outlook Express: There was an error opening this message)
(The Address Book failed to load. OE is incorrectly configured)
(Corrupted or mismatched WAB32.DLL file)
http://support.microsoft.com/?kbid=239135
OLEXP: Error Message: Address Book Failed to Load
(There was an error opening this message)
http://support.microsoft.com/?kbid=269777
http://support.microsoft.com/?kbid=310873
OLEXP: MSIMN Caused an Invalid Page Fault in Module Wab32.dll
http://support.microsoft.com/?kbid=247706
Err Msg: Address Book Failed To Load, Outlook Express Is...
http://support.microsoft.com/?kbid=191946
Err Msg: Unable to Open Address Book, a Component Is Missing
http://support.microsoft.com/?kbid=192321

The Windows Address Book (WAB)
http://www.insideoe.com/files/wab.htm

To share Contacts between Outlook and Outlook Express
http://www.slipstick.com/contacts/oeshare.htm
--
Bruce Hagen
MS-MVP Outlook Express
Imperial Beach, CA


"SteveH" wrote in message
...
Hi, hope someone can help. I use outlook express for my emails and after
the
recent windows explorer update to version 7 I have been able to receive my
mail but unable to send. The message that appears states that the address
book is not installed properly. This blocks me from sending any replies or
even creating a new mail. Any ideas whats causing this or how to remove
the
problem without resorting to a hammer! I am running windows XP and have
already installed the Sp2 version. Help!
Steve