Get HTTP Error 500 only when I edit Items in K2 Dashboard

Hi,

Today i have installed the quickStart Template Financial Businnes, without problems.
But I got HTTP 500 Error when i edit anything in the K2 Dashboard.

I have no Problems when i change standard Joomla Menus, Articls an so on.

Please help
Markus Lehmann

! K2 requires multi-byte string array functions (php) to be enabled. !

Now, it runs

You can see it help / systeminfo / PHP Settings / Mbstring Enabled: Yes !!!