Samsung Galaxy S2 internal storage problem

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http://androidforums.com – I've been using my phone for about 5 months but recently I faced a problem with the internal storage of my phone. I have a total space of 1.97GB for my internal storage, apps used up 601MB and it says I only have 216MB available. Adding up the apps and available spaces, I should have about 1GB left. I don't know where it go and I can't update my apps now due to the insufficient space. So does anyone know how I can deal with this problem? Thanks a lot for your time. (General)