File Manager Doubleclick Error

Since I made the Update to 3.51 and I doubleclick a text-file or something I get the error message:
Download failed:
I always have to use the edit button to look at a file.

And in Usermin the whole File Manager Does not work at all. It shows up an Error window with a lot of content
Failed to get language list:
.
.
.
It shows HTML contet. I could not copy it. But i could make a screen print if you need.