Redmine

I'm a bit stuck trying to integrate Git in advanced mode using this tutorial http://www.redmine.org/projects/redmine/wiki/HowTo_configure_Redmine_for_advanced_git_integration

Everything was working fine until I tried to add Access Control to my repositories (prior to that I was able to clone and update repositories via Grack without any problem).

Here is my Apache Vhost (i've replaced sensitive information with place-holders eg: username, password) :

<VirtualHost *:8081>
    ServerName git.domain.com
    DocumentRoot "/opt/grack/public" 
    <Directory "/opt/grack/public">
        Options None
        AllowOverride None
        <IfVersion < 2.3 >
        Order allow,deny
        Allow from all
        </IfVersion>
        <IfVersion >= 2.3>
        Require all granted
        </IfVersion>
     </Directory>
     PerlLoadModule Apache::Redmine
    <Directory "/opt/grack/public">
        Options None
        AllowOverride None
        <IfVersion < 2.3 >
        Order allow,deny
        Allow from all
        </IfVersion>
        <IfVersion >= 2.3>
        Require all granted
        </IfVersion>
     </Directory>
     <Location "/">
        RedmineGitSmartHttp yes
       AuthType Basic
       AuthName "Redmine git repositories" 
       Require valid-user
       PerlAccessHandler Apache::Authn::Redmine::access_handler
       PerlAuthenHandler Apache::Authn::Redmine::authen_handler
       RedmineDSN "DBI:Pg:database=redmine;host=localhost" 
       RedmineDbUser "username" 
       RedmineDbPass "password" 
       #AuthUserFile /dev/null
     </Location>
        LogLevel debug
        ErrorLog ${APACHE_LOG_DIR}/error_git.log
        CustomLog ${APACHE_LOG_DIR}/access_git.log combined
 </VirtualHost>

When I try to clone my repository http://Server_IP:8081/myrepo with git here is what I get

Cloning into 'myrepo'...
fatal: unable to access 'http://xx.xx.xx.xx:8081/myrepo/': The requested URL returned error: 500

and the corresponding Apache log output is

AH00027: No authentication done but request not allowed without authentication for /myrepo/info/refs. Authentication not configured?

Where should I start to try and find the cause of this error ?

Thanx in advance