As you can see in my fstab, the last line is : #Data /mnt/Data vboxsf defaults 0 0
Data exist from time to time /mnt/Data always exists. I have to comment that line in order to boot my system. Else, instead of showing the mount error, and continue booting, the system shows an emergency prompt, and is unable to boot. I think that is a real problem that a sysetm is unable to boot just because a data partition is not accessible. The behaviour with sysvinit was smarter. Regards.
