Unknown modifier 't'

Hi, I'm getting following error, I'm not really sure why:
Warning: preg_replace() [function.preg-replace]: Unknown modifier 't' in /include/functions.php on line 2084

This is following line:

$url_query = preg_replace('/(.*?)/strona-([0-9]*)-/', '$1/strona-'.$counter.'-', $targetpage); 

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Thanks for any help.