warning: strcmp() expects parameter 2 to be string, array given in system.module

You probably have a misbehaving module in your installation, which implements hook_requirements() in a broken way.

livespots, your patch fixed stopped the error for me too.

php 5.3.3

function _system_sort_requirements($a, $b) {
  if (!isset($a['weight'])) {
    if (!isset($b['weight']) && isset($a['title']) && isset($b['title'])) {
      return strcmp($a['title'], $b['title']);
    }
    if(isset($b['weight'])){
      return -$b['weight'];
    }
  }
  if(isset($a['weight'])){
   return isset($b['weight']) ? $a['weight'] - $b['weight'] : $a['weight'];
  }
}

#2 also worked for me... is this fixing something or just a band aid hack?

This is most likely what was described in #1 so this patch is really just a band-aid. I'm getting the errors too on D7, I will try tracking down the module causing this.

Also that patch is overwriting the information that is passed to the function.

I'm tracking this error too (drupal 6.22 with wampMSS to test PHP5.3)

What do you thing about system module at line 1725 :

// Check run-time requirements and status information.
$requirements = module_invoke_all('requirements', 'runtime');
usort($requirements, '_system_sort_requirements');

this is a duplicate of this #933684: Same requirements from different modules causes warnings in _system_sort_requirements()

warning: strcmp() expects parameter 2 to be string, array given in...
Resolved serializing arrays:

/**
 * Helper function to sort requirements.
 */
 
function _system_sort_requirements($a, $b) {
  if (!isset($a['weight'])) {
    if (!isset($b['weight'])) {
-     return strcmp($a['title'] ,$b['title']);
+     return strcasecmp(serialize($a['title']), serialize($b['title']));
    }
    return -$b['weight'];
  }
  return isset($b['weight']) ? $a['weight'] - $b['weight'] : $a['weight'];
}