ISP blocked due to abuse?

Well, it seems today that I'm now unable to post anything over at the 4chan imageboards, otherwise I get this message:
"Posting from your ISP has been blocked due to abuse. [More Info]"
I can still browse the site, all the images and threads load fine, I just can't post. What gives? I've never posted spam or porn.

>>201
just asked a friend if he could post, he told me he couldn't he is also portuguese and different isp. seriously, why don't you ban only the ip's instead of the whole country.