If Kies tells you that you have a unofficial release it usually means that you have an unofficial release. :) This is usually the result of flashing the device with heimdall/odin and an prerelease firmware that was never official released for you device and/or region. But there can be other reasons for this too.
You could flash an offical ROM, which can be obtained for example from samfirmware.com. Instructions on how-to flash and what release is the current offical for your region can be found on this site too. Be aware that flashing can leave you device in an unusable state and it will do a factory reset, so save your data prior flashing. Also you may lose your warranty.