warning: array_merge() [function.array-merge]: Argument #2 is not an array

Can you please paste an export of the page you created that is demonstrating this error?

Also receiving this error on my site, here is the export

$page = new stdClass;
$page->disabled = FALSE; /* Edit this to true to make a default page disabled initially */
$page->api_version = 1;
$page->name = 'lz_tv_commericals';
$page->task = 'page';
$page->admin_title = 'LZ TV Commercials';
$page->admin_description = 'LegalZoom TV commercials';
$page->path = 'press-center/press-media/tv';
$page->access = array();
$page->menu = array(
  'type' => 'normal',
  'title' => 'TV Commercials',
  'name' => 'secondary-links',
  'weight' => '0',
  'parent' => array(
    'type' => 'none',
    'title' => '',
    'name' => 'navigation',
    'weight' => '0',
  ),
);
$page->arguments = array();
$page->conf = array();
$page->default_handlers = array();
$handler = new stdClass;
$handler->disabled = FALSE; /* Edit this to true to make a default handler disabled initially */
$handler->api_version = 1;
$handler->name = 'page_lz_tv_commericals_panel_context';
$handler->task = 'page';
$handler->subtask = 'lz_tv_commericals';
$handler->handler = 'panel_context';
$handler->weight = 0;
$handler->conf = array(
  'title' => 'Panel',
  'no_blocks' => FALSE,
  'css_id' => '',
  'css' => '',
  'contexts' => array(),
  'relationships' => array(),
);
$display = new panels_display;
$display->layout = 'onecol';
$display->layout_settings = array();
$display->panel_settings = array();
$display->cache = array();
$display->title = 'TV Commericals';
$display->hide_title = FALSE;
$display->title_pane = 0;
$display->content = array();
$display->panels = array();
  $pane = new stdClass;
  $pane->pid = 'new-1';
  $pane->panel = 'middle';
  $pane->type = 'node';
  $pane->subtype = 'node';
  $pane->shown = TRUE;
  $pane->access = array();
  $pane->configuration = array(
    'nid' => '2682',
    'teaser' => 0,
    'links' => 1,
    'leave_node_title' => 0,
    'identifier' => '',
    'override_title' => 1,
    'override_title_text' => '<none>',
  );
  $pane->cache = array();
  $pane->style = array();
  $pane->css = array();
  $pane->extras = array();
  $pane->position = 0;
  $display->content['new-1'] = $pane;
  $display->panels['middle'][0] = 'new-1';
  $pane = new stdClass;
  $pane->pid = 'new-2';
  $pane->panel = 'middle';
  $pane->type = 'views_panes';
  $pane->subtype = 'lz_tv_commercials-panel_pane_1';
  $pane->shown = TRUE;
  $pane->access = array();
  $pane->configuration = array(
    'context' => array(
      '0' => 'context_node_1',
    ),
  );
  $pane->cache = array();
  $pane->style = array();
  $pane->css = array(
    'css_id' => 'tv-commercial',
    'css_class' => '',
  );
  $pane->extras = array();
  $pane->position = 1;
  $display->content['new-2'] = $pane;
  $display->panels['middle'][1] = 'new-2';
  $pane = new stdClass;
  $pane->pid = 'new-3';
  $pane->panel = 'middle';
  $pane->type = 'views_panes';
  $pane->subtype = 'lz_tv_commercials-panel_pane_2';
  $pane->shown = TRUE;
  $pane->access = array();
  $pane->configuration = array(
    'context' => array(
      '0' => 'context_node_1',
    ),
  );
  $pane->cache = array();
  $pane->style = array(
    'style' => 'grey',
  );
  $pane->css = array(
    'css_id' => 'commercials-carousel',
    'css_class' => '',
  );
  $pane->extras = array();
  $pane->position = 2;
  $display->content['new-3'] = $pane;
  $display->panels['middle'][2] = 'new-3';
$handler->conf['display'] = $display;
$page->default_handlers[$handler->name] = $handler;

I have two pages set up, the above export and a similar page that takes a Node argument. Both invoke a panel
pane (via views_content_pane) that has an optional argument via Node Context.

In panels/includes/plugins.inc on line 50

 if (!$context) {
    $context = new ctools_context;
 }   

If there is no context passed in, panels will constructs a new context object. It is then passed down to

<?php

/*
...
 * @param $context
 *   An array of context objects available for use.
..
 */
function ctools_content_render($type, $subtype, $conf, $keywords = array(), $args = array(), $context = array(), $incoming_content = '') {

which is expecting an array of contexts, not just one context object. This eventually causes a problem when
ctools_context_optional->add_empty tries to array_merge it.

I believe the fix is to create an array consisting of a new unknown object which is actually a panels issue.

I opened a panels issue and posted a patch: here http://drupal.org/node/624710

Related issue http://drupal.org/node/624710 was fixed. Patch accepted. Setting this to fixed.