Fatal error: Class 'CI_Model' not found in

[eluser]Unknown[/eluser]
I have fblmodel.php that is being used throughout my site with no problems. Yesterday a strange bug appeared that only occurs when one particlular function within the fblmodel.php is called by the controller.

previously this particular fuunction ran correctly. I dont believe I changed anything but anything is possible !!

The error I get on screen is as follows:

A PHP Error was encountered

Severity: Notice

Message: Unknown: Internal error occurred. Refer to server log for more information. [2012-02-10 08:54:09] (errflg=2)

Filename: Unknown

Line Number: 0

and the error in the server logs is

Fatal error: Class 'CI_Model' not found in line 3

Any help would be apprciated..

I dont think its relevant but I will include the function in question for refernece:

Code:

function cron_check_email_verification($domain, $proxies, $maxProxyArray)
{
  
  //set up our variables..
  $mailserver = $domain['domainUrl'];
  $port = "143/novalidate-cert";
  $user = "contact@".$domain['domainUrl'];
  $pass = $domain['emailPassword'];
    
  if ($mbox = imap_open( "{" . $mailserver . ":" . $port . "}INBOX", $user, $pass ))
  {  
   //lets get the verification emails from aol...
   $aolVarificationEmails = imap_search($mbox, 'BODY "http://postmaster.aol.com/confirm.php?code="', SE_UID);
  
   print_r($aolVarificationEmails);
  
   if($aolVarificationEmails[0])
   {
    foreach($aolVarificationEmails as $email)
    {
     //get the confirmation link
     $emailBody = imap_fetchbody($mbox, $email, '1',FT_UID);
     $theConfirmationLink = 'http://postmaster.aol.com/confirm.php?code='.$this->get_string_between($emailBody, "http://postmaster.aol.com/confirm.php?code=", '"');
    
     //initiate cUrl
     $ch = $this->curlinit();
    
     //click the link...
     $referer = 'http://'.$mailserver;
     $s = $this->curlget($ch, $theConfirmationLink, $referer);
    
     //check for success..
     $startsAt = strpos($s, "Thank you for ") + strlen("Thank you for ");
     $endsAt = strpos($s, " your Support Request", $startsAt);
     $test = substr($s, $startsAt, $endsAt - $startsAt);
     if($test == 'confirming')
     {
      //delete the message..
      imap_delete ( $mbox , $email , FT_UID );
      imap_expunge ( $mbox );
      $result = 'done';
     }
     else
     {
      $result = 'fail';
     }
    
     //close the curl connection..
     curl_close($ch);
    }
   }
   imap_close($mbox);
  
  }
  else
  {  
   print_r(imap_errors());
   exit ("Can't connect: " . imap_last_error() ."\n");  
   echo "FAIL!\n";  
  };


  
  return $result;
}