Default theme not found.

I have just installed Dotclear and I get this error when browsing to https://localhost/dotclear/:
Default theme not found.
This either means you removed your default theme or set a wrong theme path in your blog configuration. Please check theme_path value in about:config module or reinstall default theme. (default)

And if I login to the admin, I get this:
Fatal error: Uncaught exception 'Exception' with message 'Table 'dotclear.dc_pref' doesn't exist (1146)' in /usr/share/dotclear/web/inc/libs/clearbricks/dblayer/class.mysql.php:105 Stack trace: #0 /usr/share/dotclear/web/inc/libs/clearbricks/dblayer/class.mysql.php(116): mysqlConnection->db_query(Resource id #15, 'INSERT INTO `dc...') #1 /usr/share/dotclear/web/inc/libs/clearbricks/dblayer/dblayer.php(376): mysqlConnection->db_exec(Resource id #15, 'INSERT INTO `dc...') #2 /usr/share/dotclear/web/inc/libs/clearbricks/dblayer/class.cursor.php(233): dbLayer->execute('INSERT INTO `dc...') #3 /usr/share/dotclear/web/inc/core/class.dc.workspace.php(262): cursor->insert() #4 /usr/share/dotclear/web/admin/index.php(49): dcWorkspace->put('doclinks', true, 'boolean', '', NULL, true) #5 {main} thrown in /usr/share/dotclear/web/inc/libs/clearbricks/dblayer/class.mysql.php on line 105

So I installed Dotclear manually in /var/www/ and it works perfectly.

ProblemType: Bug
DistroRelease: Ubuntu 12.04
Package: dotclear 2.4.2+dfsg-1
ProcVersionSignature: Ubuntu 3.2.0-24.37-generic 3.2.14
Uname: Linux 3.2.0-24-generic i686
ApportVersion: 2.0.1-0ubuntu7
Architecture: i386
Date: Thu May 17 00:32:10 2012
PackageArchitecture: all
ProcEnviron:
 LANGUAGE=fr_FR:en
 TERM=xterm
 PATH=(custom, no user)
 LANG=fr_FR.UTF-8
 SHELL=/bin/bash
SourcePackage: dotclear
UpgradeStatus: Upgraded to precise on 2012-04-27 (19 days ago)