Date Range - Loading forever

Hi everybody,
I just noticed that the plugin I’ve build is loading forever, when I set a Date Range. Everything else (year, month, week, day) is working fine. I am using piwik 1.12. I am almost sure that this had worked in an earlier version of piwik, but don’t know which one exactly. So has anybody an idea what could be wrong?

can be closed. Found a problem with a datestring.