Samsung Galaxy S2 not enough storage
There was a thread similar to yours a while back. It refered to a Stackoverflow thread with a overwhelmingly positive answer.
One of the answers is to clear dumpstack. Here is the excerpt from the Stackoverflow answer.

Here's a very simple solution that works on my Samsung Galaxy S II and NOTE 1 ; I have no idea about other models:
Open the Phone app and switch to Keypad.
Dial *#9900#
On the screen that appears, click on the button labelled &quot;Delete dumpstate/logcat&quot;.

I've restored about one GB of system space this way.

Hope this solves your problem.