[TYPO3-english] Multishop extension: depricated method

[TSniper]

Hello,

i have installled the last version of Multishop v4.0.2, i'm using 7.6.6 Typo3 version, but i have this error in frontend:

#1: PHP Runtime Deprecation Notice: Non-static method mslib_befe::strtolower() should not be called statically, assuming $this from incompatible context in ...\typo3conf\ext\multishop\pi1\class.tx_multishop_pi1.php line 125 (More information)

TYPO3\CMS\Core\Error\Exception thrown in file
...\typo3\sysext\core\Classes\Error\ErrorHandler.php in line 111.

Can anybody help me please resolving this ?