Other people using the same IPs. Change servers until you find one that works .
Another solution is 9xbuddy, just copy the link and you'll get different options (choose "ORIGINAL - /2" or "BACKUP - ORIGINAL")
Pixeldrain increased the daily limit to 20gb that is way better than they lame 5gb. I bet they got 2 or 3 more servers to handle all the traffic and more uploads.