This post describes solution for mounting error (error 6). By some reason Linux cannot mount one or more file systems though boot partition starts without any problems. On Fedora Linux this symptom is really confusing because it additionally dumps error about ext3 label problem.
mkrootdev. Label / not found
This is not file system problem. In my case labels existed and partition didn’t contain any errors. Solution was very simple. Problem disappeared after changing “SATA Controller Mode” from “Enhanced” to “Compatible”.