This happened to me also. What I did (and that solved my problem) was to open my SkyrimPrefs.ini and change my iBlurDeferredShadowMask from 3 to 6. Try it and tell me if it works!
EDIT: If it doesn't work, but if it reduces the amount of checkering, you could always try a higher value. I have 99,9% of sure that that's what's causing your shadows to be like this.
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http://skyrim.nexusmods.com/Images/115367
When that gets resolved I'll be able to do so.
EDIT: If it doesn't work, but if it reduces the amount of checkering, you could always try a higher value. I have 99,9% of sure that that's what's causing your shadows to be like this.
Low and medium lead to a lot of checkering like that.
High and Ultra pretty much clear it up! Give that a shot.