I see your original post was almost a year ago. Evidently the new spark plugs fixed your alert message. I decided to look around for other causes for the check hybrid system alert.I did not have the warning back on again. The car is now at 127,000 miles. The spark plugs were changed at 85,000 miles.
1. press the display button so the MID will show the Energy Monitor. (battery and tire) Make sure the battery shows a 15% or higher charge. If it will charge to 80% this should show the traction battery is ok.
2. A low charged or weak 12 volt battery in the trunk can also activate the VSC and check hybrid system alerts. Best to let the car sit overnight, then using a dc voltmeter check across the terminals to see if it reads 12 volts. A cheap digital meter may read more accurate. With the engine running it should read about 14 volts dc or slightly above that.
The auto stores sell a power outlet indicator consisting of led colored lights showing basically if the 12 volt battery is good. Some may have the lights plus a voltage reading.
3. running out of gas can also activate these alerts. To reset, remove the negative terminal on the 12 volt battery to reset the hybrid system.