Media stored on External Hard drive crashes computer when in sleep mode.

I'm storing media on Lacie rugged and it's connected to my computer via firewire 800. When I return from an editing break and move the FCP playhead the computer crashes and I get the rotating colored circle. During this time the disk is not spinning and I'm unable to force quit the application. My current work around is restarting the computer. As for troubleshooting, in System Preferences > Energy Saver, I've unchecked the option "put the hard disk(s) to sleep when possible".
I've also confirmed that the external hard disk is formatted as Mac OS Extended
Does anyone know the possible cause of this issue? Any information is greatly appreciated.

Thanks!