wp-piwik stopped working

I can’t really say when exactly it stopped working, but all my sites (both singles and MU) do no longer show visits on the admin dashboard (but they are registered, piwik shows them on its own site).

Also, after adding a new site to my MU installation it tried to activate the wp-piwik plug in. I got the following error:

Das Plugin kann nicht aktiviert werden, da es einen fatalen Fehler erzeugt.

Parse error: syntax error, unexpected T_STRING in XXXXX/wp-content/plugins/wp-piwik/wp-piwik.php on line 755

https://www.ads-software.com/plugins/wp-piwik/