How to resolve fatal error 'Cannot redeclare commerce_kickstart_preprocess_html'? I have installed an ecommerce website with Commerce Kickstart, not in demo  mode. Everything was OK and I began to add products and then my problem started; when I click on 'products category' I receive this error message:


  Fatal error: Cannot redeclare commerce_kickstart_preprocess_html() (previously declared in /homepages/44/d576739206/htdocs/profiles/commerce_kickstart/themes/commerce_kickstart_theme/template.php:41) in /homepages/44/d576739206/htdocs/profiles/commerce_kickstart/themes/commerce_kickstart_theme/template.php on line 41    


This is what that line 41 (as in the error message) looks like.

function commerce_kickstart_preprocess_html(&amp;$variables) {
  drupal_add_css('http://fonts.googleapis.com/css?family=Lobster+Two:400,700', array('type' =&gt; 'external'));
}    


What could the problem be? How can I solve it?

Update (as in one of the comments): I tried to change as you said it and I have this message:

Fatal error: Cannot redeclare commerce_kickstart_theme_preprocess_html() (previously declared in /homepages/..../htdocs/profiles/commerce_kickstart/themes/commerce_kickstart_the‌​me/template.php:9) in /homepages/..../htdocs/profiles/commerce_kickstart/themes/commerce_kickstart_the‌​me/template.php on line 41 code

Update 2 : So if I use another theme, the problem is solved. 
And there are 2 (minor) differences in the new error message : 
Now it is in that line "9" (no longer "41") : 

function commerce_kickstart_theme_preprocess_html(&amp;$variables) { // Add conditional stylesheets for IE drupal_add_css(path_to_theme() . '/css/commerce-kickstart-theme-ie-lte-8.css', array('group' =&gt; CSS_THEME, 'weight' =&gt; 23, 'browsers' =&gt; array('IE' =&gt; 'lte IE 8', '!IE' =&gt; FALSE), 'preprocess' =&gt; FALSE)); drupal_add_css(path_to_theme() . '/css/commerce-kickstart-theme-ie-lte-7.css', array('group' =&gt; CSS_THEME, 'weight' =&gt; 24, 'browsers' =&gt; array('IE' =&gt; 'lte IE 7', '!IE' =&gt; FALSE), 'preprocess' =&gt; FALSE));

Update 3 : Here is template.php :

&lt;?php
/**
 * Preprocess variables for html.tpl.php
 *
 * @see system_elements()
 * @see html.tpl.php
 */
function commerce_kickstart_theme_preprocess_html(&amp;$variables) {
  // Add conditional stylesheets for IE
  drupal_add_css(path_to_theme() . '/css/commerce-kickstart-theme-ie-lte-8.css', array('group' =&gt; CSS_THEME, 'weight' =&gt; 23, 'browsers' =&gt; array('IE' =&gt; 'lte IE 8', '!IE' =&gt; FALSE), 'preprocess' =&gt; FALSE));
  drupal_add_css(path_to_theme() . '/css/commerce-kickstart-theme-ie-lte-7.css', array('group' =&gt; CSS_THEME, 'weight' =&gt; 24, 'browsers' =&gt; array('IE' =&gt; 'lte IE 7', '!IE' =&gt; FALSE), 'preprocess' =&gt; FALSE));

  // Add external libraries.
  drupal_add_library('commerce_kickstart_theme', 'selectnav');
}

/**
 * Implements hook_library().
 */
function commerce_kickstart_theme_library() {
  $libraries['selectnav'] = array(
    'title' =&gt; 'Selectnav',
    'version' =&gt; '',
    'js' =&gt; array(
      libraries_get_path('selectnav.js') . '/selectnav.min.js' =&gt; array(),
    ),
  );
  return $libraries;
}

/**
 * Override the submitted variable.
 */
function commerce_kickstart_theme_preprocess_node(&amp;$variables) {
  $variables['submitted'] = $variables['date'] . ' - ' . $variables['name'];
  if ($variables['type'] == 'blog_post') {
    $variables['submitted'] = t('By') . ' ' . $variables['name'] . ', ' . $variables['date'];
  }

function commerce_kickstart_theme_preprocess_html(&amp;$variables) {
drupal_add_css('http://fonts.googleapis.com/css?family=Lobster+Two:400,700', array('type' =&gt; 'external'));
 }
}
Because the two file paths are the same file, it suggests a possible problem with your op-code caching.

Check if you have any PHP op-code cache enabled; you should only have one op-code cache utility and may need to disable one.

You may also need to tweak your APC settings (if enabled).

apc.include_once_override = 0


Check also https://stackoverflow.com/questions/4575341/php-with-apc-fatal-errors-cannot-redeclare-class.