In Ubuntu tweak 0.8.7 which is installed in my Ubuntu 14.04 LTS running unity I could not delete a particular file called 'fail' in the thumbnail cache. I am actually trying to remove that file with the 'Janitor' feature that is available with Ubuntu tweak. Every time I try deleting that file Ubuntu tweak crashes(i.e. closes). Why does this happen and how to delete it? By the way I could delete every other thumbnail cache file and also other kind of cache except this 'fail' file. Below is a screen shot:-