Update-Problem: Warning - preg_match(): Unknown modifier 'w' (2 replies)

Hello from Germany,

I got the message that there is an update for piwik to Version 2.12 and made it with the autoupdate-function.
Before that, everything works fine and i had no error messages.

Now there comes up:
WARNING: /mnt/webj/e1/43/51186643/htdocs/WebAnalyse/core/Url.php(252): Warning - preg_match(): Unknown modifier 'w' - Piwik 2.12.0
and the Javascript-Tracking-Code should be integrated, but it still is!

I made no changes to the directory in which the files are stored. The config.ini.php is correctly set to my URL: "marcmertens.photography/WebAnalyse" Caused by this error I load up the files with FileZille another time manually.

Piwik should be used for my own Wordpress-Blog under: QuerKommentar.de and there i use the WP-Piwik-PlugIn.

PS:
I am new with Piwik and just started the tool. So I have still to learn a lot of things about it.
Thanks for the support and time.

Greetings,
Marc