[Columbine]

I've had a tub of that in my fridge i've been using for just about the same length of time. Miso lasts for ages if kept right. You didn't say if it was in an air-tight container or not. Either way check that there is absolutely no mould on it or that it doesn't smell/taste musty (if it does, throw it out), and as komitsuki said, it it's been exposed to air for a long time, remove that layer. If the whole surface has been exposed the whole time, or completely caked, cracked and dried out, you may as well throw it out because you might not be able to tell if other things have dripped into it or not and there's not much you can do to resurrect dried paste.