Changing Logo not working (no replies)

Hi,

I have Piwik running on Mac OS X Server 10.10.3 and when I try to change the logo it does not work.

I click the button, select the png image file and click choose. Nothing happens from that point?

In the browser I see an error

Failed to load resource: the server responded with a status of 500 (Internal Server Error) - https://SERVERURL/index.php?module=CoreAdminHome&format=json&action=uploadCustomLogo

I have looked in the forums but afraid I didn't find anything

Thanks in advance