People who get this error. The problem solved beneath.
You should not be running with PHP 6.0. First of all, it's an unreleased test version, and is not considered ready for any kind of production use. Second, osC makes use of many of the functions that PHP is removing in PHP 6.0, among them get_magic_quotes_gpc() (there seems to be some discussion about putting that one back in). Read this: us.php.net/ma....deprecated.php . As of PHP 5.3, they will generate "deprecated" errors, warning you to upgrade your code.
What you can try to do is Install joomla 1.7 and marvikShop 2.0, maybe problem has been solved. Some other point is to eleminate this function to test. Because is it undefined. Just put // before this fuction and looks what happend.