checkout error with cc.php

[RoninS14]

I get this warning message at the top:

 

Warning: str_repeat() [function.str-repeat]: Second argument has to be greater than or equal to 0 in /usr/www/users/tahiti/includes/modules/payment/cc.php on line 137

 

 

and this is what line 137 is:

 

$confirmation = array('title' => $this->title . ': ' . $this->cc_card_type,
						  'fields' => array(array('title' => MODULE_PAYMENT_CC_TEXT_CREDIT_CARD_OWNER,
												'field' => $HTTP_POST_VARS['cc_owner']),
										  array('title' => MODULE_PAYMENT_CC_TEXT_CREDIT_CARD_NUMBER,
Line 137									   'field' => substr($this->cc_card_number, 0, 4) . str_repeat('X', (strlen($this->cc_card_number) - 8)) . substr($this->cc_card_number, -4)),
										  array('title' => MODULE_PAYMENT_CC_TEXT_CREDIT_CARD_EXPIRES,
												'field' => strftime('%B, %Y', mktime(0,0,0,$HTTP_POST_VARS['cc_expires_month'], 1, '20' . $HTTP_POST_VARS['cc_expires_year'])))));

[RoninS14]

any advise on what this could be and how to fix it?