Joomla error at the end of the checkout process

-- url of the page with the problem -- : die-besten-weine-der-welt.de.dd26820.kasserver.com/
-- HikaShop version -- : 2.2.1
-- Joomla version -- : 3.1.5
-- PHP version -- :5.3.18-nmm1

hi, when completing the last step of the checkout process, customers get the following error message:
Warning: explode() expects parameter 2 to be string, array given in /www/htdocs/w010b858/libraries/joomla/string/punycode.php on line 189

Hi,

I don't know where this comes from but you can turn off the "error reporting" option of the joomla configuration to remove its display.