Drupal's default search won't search in Solr
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I'm struggling for few weeks now with Solr and Drupal but I can not resolve this : 
I have a Solr.3.6 running on a Tomcat6 server in local. 
Everything works fine I can commit data and make queries in Solr admin.

I wish to make this Solr my Drupal7 default search on my website (not to index drupal's content but only to use Drupal as a search plateforme). So I installed apachesolr-7.x-1.0-rc2 module. I can connect Solr without error and enable it as the default search. 

But when I'm making a research it returned several errors : 


    Warning: htmlspecialchars(): Invalid multibyte sequence in argument in check_plain() (line 1572 of /var/www/drupal-7.14/includes/bootstrap.inc).
    Warning: htmlspecialchars(): Invalid multibyte sequence in argument in check_plain() (line 1572 of /var/www/drupal-7.14/includes/bootstrap.inc).

    The Apache Solr search engine is not available. Please contact your site administrator.

Can someone tell me what can cause this ? And why in my apachesolr module settings, Drupal can connect to my Solr but not when I'm using the default search.

I have the exact same error using Drupal6

Thank you for your help
