Can't connect to backend: No such file or directory

Greetings all,

since yesterday my plesk wont work right anymore. I got one E-Mail where it says plesk update gone wrong. (But when i click on the link inside the mail, it cant find the file).

So i go inside Plesk and click on update -> Can't connect to backend: No such file or directory.

What can i do now to fix Plesk?