warning: Invalid argument supplied for foreach()..on line 1190.

CCK fields can be indexed using the 6.x-1.0 branch. Anyway, here is a quick band-aid fix for the problem.

best to follow coding standards and indent.

Looks ok for 6.2.

Let's confirm it's not an issue in the other branches.

I'm a little bit confused. 6.x-2.x shows that $params['fq'] is a 2 level nested array.

$params['fq'][$delta][] = $value;

But in 5.x-2.x (6.x-1.x) seems to be only a 1 level deep. In apachesolr_search.module is handled:

  if (('' == $keys) && isset($params['fq'])) {
    // Move the fq params to the q.alt for better performance.
    $params['q.alt'] = implode(' ', $params['fq']);
    unset($params['fq']);
  }

Digging a little bit in 6.x-2.x-dev I found that next part is missed in apachesolr_modify_query() from 6.x-1.x and 5.x-2.x which seems to be critical on subqueries....

  if ($filter_queries = $params['fq']) {
    foreach ($filter_queries as $delta => $value) {
      $fq = $tag = '';
      $op = 'AND';
      // CCK facet field block deltas are not the same as their Solr index field names.
      $cck_delta = '';
      if (strpos($delta, '_cck_')) {
        $cck_delta = trim(drupal_substr($delta, 7, drupal_strlen($delta)));
      }
      if (in_array($delta, $ors) || in_array($cck_delta, $ors)) {
        $tag = "{!tag=$delta}";
        $op = 'OR';
      }
      $fq = implode(" $op ", $params['fq'][$delta]);
      $params['fq'][] = $tag . $fq;
      unset($params['fq'][$delta]);
    }
  }

This part transform $param['fq'] from a 2 level to an one level array.

Discussion needed...

Ok - that's all related to OR facets. So let's not backport this as it's pretty complicated and disruptive.