What would cause Unable To Verify Volume message

I will include the message that occurs during Perfect Disk 12.5 boot time defrag.

When I use windows tools to check the disk no errors are found, however this check is performed with windows active. In the old days of XP you could Run ChkDsk C:\ and do an offline check. It appears you can no longer do that in Windows 8? Plus, I came across one JPG file which the computer cannot read, apparently. Normally you'd want to verify the disk offline.