Eu precisava especificar a porta do catálogo global no AuthLDAPURL. Eu tenho que trabalhar usando a configuração abaixo:
<Location /svn>
DAV svn
AuthType basic
SVNParentPath /srv/repos/svn
AuthName "helloworld"
AuthBasicProvider ldap
AuthLDAPURL "ldap://192.168.1.10:3268/dc=example,dc=com?sAMAccountName" NONE
AuthLDAPBindDN "CN=subversion,CN=users,DC=example,DC=com"
AuthLDAPBindPassword "secret"
Require ldap-group CN=svn,OU=groups,DC=example,DC=com
</Location>