Default memory full ?!?!

sup Guys,

Need ur helps at that, can't figure out, where the problem is.

So ... At my phone, it just shows permanently, that my memory is full.
But how can that happen, when I just have Nova launcher, Facebook, Whatsapp and SwiftKey on my phone? I can't update apps at all, can't install new apps, tried so many ways to fix that, like wipe etc. I am on Sammy stock Rom 4.1.2 ... Do you guys think, that is a firmware bug? That's strange, I never faced a problem like this.

Appreciate any help
CURRENT ANDROID: SAMSUNG GALAXY S2 ( i9100 )

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