I found a PNG pixelated image on the net (16*16) and under the "Filters" blur effect are grayed out and unclickable. Even when I size it up it still doesn't get blurred (which happens by default). I'm using a Gimp version on Edubuntu titled "2.2.13-1ubuntu4.4 (gimp)" and I'm not able to install a newer one. So far this is the only image where some features doesn't seem to work. I reopened it a couple of times and it's always the same. What seems to be the problem?
Some effects like blur can not be applied on indexed formats. You will have to change the image mode to RGB first.
In Gimp this is done by selecting Image > Mode > RGB from the top menu bar.