we have a problem that we get a internal server error on about every ajax call. The example below happens when editing a view clicking "add filter" and directly click on abort. It also happens when making changes to a view. At first glance the change seemed to be ignored but after refreshing the pages the changes will be visible.
When accessing the URL which throws the error we get a valid json string (checked with jsonlint.com).
Our server logs sadly show nothing interesting. I would appreciate any kind of hint where to look for a solution.
Edit: The nojs version seems to work fine but that's no solution in the long term :/