Cannot send mail: A problem occurred while trying to open this message

Split from this thread. 

My WLM no longer allow me to send ANY email.  This occurred this morning after the latest Windows update.  Windows updates have a disturbing habit of breaking things, I've found, though they usually go away after turning the computer off and back on.  This time it is persistent.  The error message is very simple: "A problem occurred while trying to open this message.  {new line} A problem has occurred. Please try again."  This happens when I try to reply or forward a message, or create a new one.  Help!