Well.. i had an installation with motion running as webcam-server .. i reinstalled the linux-distro and reinstalled motion, now the root have no access to the webcam. The "pi" user still can access and work with the webcam, but the "pi" user only. Is there a way to change rights for connected webcams? -- Already reinstalled motion .. didn't help!
Thank you!

/dev/directory? Does that device file have the required permissions? Look for the permission of the original device file and not any symlink that it may have. – Lord Loh. Feb 21 at 23:17