Bug 6699 follow-up

The warn $error will issue this message if there is a message.
It's because how warn $blabla works : it does not work, you have to add ""

C4/Installer.pm

@@ -531,7 +531,7 @@ sub load_sql {
 #   errors thrown while loading installer data should be logged
     if($error) {
       warn "C4::Installer::load_sql returned the following errors while attempting to load $filename:\n";
-      warn $error;
+      warn "$error";
     }
     return $error;
 }