Under settings, the last entry is "reset". Then choose the second button "reset device". It then completely formats /home/user and /home/user/MyDocs (don't know if / is also formatted) and restores the default settings into those.

The first button "Restore settings" did not work out for me, the error was still there then.

But beware! You lose all your pictures, music and also installed apps. It needs some time, don't touch the device during this. After it has finished, when it is booting up it is like you first started is (all settings have to be done again).

Edit: It's two days now since I did this and until now I didn't run into problems anymore... However, didn't activate Developer Mode or such since then, too...