A CRJ900 crew became distracted by a FLT SPLRS caution and after an uncommanded roll the Captain was communicating with the cabin while the First Officer began a descent to FL240 when the clearance was to FL270.

Narrative

I was the pilot not flying and my First Officer was the pilot flying. Our cruise altitude was FL340; on our decent approximately at FL300 the First Officer deployed the flight spoilers; at which I noticed the airplane beginning an uncommanded roll. I immediately advised the First Officer to stow the spoilers. We then got an OB Spoiler on caution message accompanied by a FLT SPLRS caution message. At this point I was still working the radios and trying to access the problem; as well as communicate with the Flight Attendant in the back who had called up. Somewhere in this mass confusion ATC gave us a clearance to FL270. I scrolled the altitude selector to FL240 and confirmed it with the First Officer; and he began the descent. As the descent was in progress I called to the Flight Attendant and communicated with her for a little bit; and then noticed the First Officer beginning a climb. I switched back over to the radios and asked the First Officer what was going on why was he climbing? He informed me that Center gave us a clearance to FL270 and Not FL240. We got to 25;800 when ATC questioned us. The First Officer and I were extremely tired from the continuous duty overnight. Our layover time was 6 hours 42 minutes; after taxi time to and from the hotel; hotel check in; we only had approximately a little over 5 hour at the hotel; which equaled approximately 3 hours of sleep. The fatigue of such a short rest period was evident on this flight. I believe with the new rest rules coming into effect soon; this will eliminate many simple mistakes like this.