Macfixit.com has a small interesting bit on a specific error that fortunately you've never seen. It involves an unmountable hard drive and when it's journaling is kaput. it wont' mount, but there's apparently a handy dandy terminal command to fix it.
The thing is it's generally unwise to use journalling on your Capture drives, namely speed issues. But if you have a drive that suddenly won't mount and flip on Repair Disk and see the Invalid Content in Journal error here's the fix.
Essentially copy this into the terminal with the appropriate name for your problematic drive:
/System/Library/Filesystems/hfs.fs/hfs.util -N /dev/disk0s2
The -N flag disables journaling on the device. You can find the device's name in Disk Utility's Info window.