Solved thanks to geoff@geoffdavis.net and george@zettai.net!!
under some circumstances not yet clear,  Iexplore 6.0 and Windows XP 6.02
the blank between " and http  in <a href=" http://votredomaine.net  produced in the rendering of  the index_html of the root of a plone site can make it inacccessible...
This blank  make the URI malformed as they are not properly escaped, (they must not contain unescaped characters below U+0021 including the space character and not above U+007E.)
The offending blank is after "string:"  in the fields of the Actions tabs of portal_actions, _syndication, _properties , or  _undo ... ; just remove them using Mozilla if you have the same problem than me with Iexplore.
(the correctiosn made It can be necessary to reboot in order that Iexplore can work properly)
----- Original Message -----
From: danielle.d-avout
To: Zope
Sent: Monday, December 16, 2002 2:08 PM
Subject: [Zope] Plone and Zope: space character in URI.....

With a brand new plone I asked, as I'm not logged
http://danielle.zettai.net/New_plone/index_html/manage_edit
I keep waiting ... the window of Iexplore 6.0 doesn't respond anymore
I notice that the title of the requested page is
http://danielle.zettai.net/New_plone/login_form?came_from=http:3A//danielle.zettai.net/New_plone/index_html/manage_edit&retry=
 
if I asked in an another window
http://danielle.zettai.net/New_plone/login_form?came_from=http://danielle.zettai.net/New_plone/index_html/manage_edit&retry=
it does work.... as it should be.. I'm asked to sign in ...
 
meanwhile I have no such problems with Mozilla
I looked at the source and I can see "irregularities"
 <a href=" http://... with a space between " and http
OK I am anyway ready to give up Plone...  I encountered too many problems already
But just to be reassured... I looked at the rendered html given by a new  Zope CMF portal (noname)
and I can see as well, only in a smaller number (1 for the index_html), the same fault.....
first it doesn't seem to have any consequences..
the link     <a href=" http://danielle.zettai.net/noname/join_form">Join</a>  is working...
but if I try to import the URL http://danielle.zettai.net/noname/ in HTml toolkit, it is turn not to answered...
at the contrary
http://danielle.zettai.net/noname/index_html will work and would also also http://danielle.zettai.net/New_plone/
 
 
 
here the comment of Tidy for  Zope CMF portal index_html
 
"URIs must be properly escaped, they must not contain unescaped characters below U+0021 including the space character and not above U+007E.
Tidy escapes the URI for you as recommended by HTML 4.01 section B.2.1 and XML 1.0 section 4.2.2.
Some user agents use another algorithm to escape such URIs and some server-sided scripts depend on that. If you want to depend on that, you must escape the URI by your own. For more information please refer to http://www.w3.org/International/O-URL-and-ident.html"