avatars on front- and back end randomly failing

I don't know what is happening ehre, I checked permissions and they are ok, but on http://zice.ro/ avatars are randomly failing. Load the site and on the left/middle part you should see missing images (a placeholder) depending on your browser, and if you refresh, you'll see some of them and others will be broken.

see screen shots please:
- http://www.diigo.com/item/image/1eygw/jhs8
- http://www.diigo.com/item/image/1eygw/rygu
- http://www.diigo.com/item/image/1eygw/08wr

and some from the back end:
- http://www.diigo.com/item/image/1eygw/v6cb
- http://www.diigo.com/item/image/1eygw/2yjr

so far it seems to happen on all blogs, not only the main blog and it is only my internal avatars that are failing. all other images seem to be fine !?

might jsut be me, but my connection is quite good at the moment. no errors to be found in the error log.