I can't upload out of proxy chanels, but I can download & open pages well?

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http://askubuntu.com – This problem is annoying me for 2 weeks! Unexpectedly, after migrating to Ubuntu I can't upload any thing via ADSL, also I can't send any comment in weblogs. The odd point if I use proxy/ant-ifilter (as in Tor or FreeGate) I can upload normally!! The upload is just my problem; Downloading files and opening pages are ok! Also when I use GPRS (mobile internet) I don't have any problem!!! There's not any problem in windows: both download and upload are ok, using ADSL line. My Line: ADSL (send rate: 512 Kbit/s, receive rate: 2048 Kbit/s) My Modem: D-Link 2520U My installed operating system (HowTos)