SLR Camera Errors
An unknown error code displayed on the camera LCD is the camera driver system advising your there if a failure in the unit. 
Most equipment failure error codes are a generic code telling you there is a fault but not what is failing.
You can apply self testing.
While camera is turned off, remove the lens and clean the body and lens contacts.
Try another lens - lenses can also cause errors.
Remove the batteries – let stand for 30 seconds then re-fit the batteries.
Re-set the camera functions, in the menu of the camera there should be a re-set function.
This will re-set the camera back to the manufacture specifications.
Check the C/F card pins – you may find a card pins are bent or damaged.
Try another card - the card may be faulty.
Check your batteries for voltage and current – low batteries can cause a error.
If you are using a USB attachment - check the USB lead and connection ports.
If it is an error caused via the PC try removing the software and re-installing.
If all the above trouble shooting does not eliminate the error you will have to bring/send the unit is for repair/inspection.
If your equipment has a power error please send in the battery and charger.
There are also many universal codes your camera may display. These codes are specific to the failure 
Camera not found
Drivers not found
Shutter error
Memory error
Device not found
Card read error
Card read error
Battery low