I would be very curious to know what exact router you have Hakkou, name and model so that we can see if there is a possible problem there. If uploads suddently stop working its usually settings in WinMX have changed from non default ports to defaults (ie; with reinstall or rerun of set up wizard in cases of hard crashes), or its going to be a port issue in the router/modem used, often this is the case the last possible problem would be the ISP which as we determined with ??? switching to 'Unable' cured this so it couldnt be the ISP.
Let me know what router you have and also what other antivirus and firewalls you use and we'll see if we can get to the bottom of this for ya.