FTP Not Working With Belkin Router?

I am attempting to upload some files to my school server will Filezilla. It worked the very first time I attempted to do this. A box popped up and read something like, " The key is unknown, this may not be the computer you think it is", there was a check box asking to approve this server and save the key. I ticked this box and everything was fine, it was connected. I disconnected from the server and went back an hour later to upload something and got this message when attempting to connect, "server has unexpectedly closed network connection", then, "unable to connect". I get it every single time I try to do this from home. However, I have been able to connect everywhere else but my house. I can connect with the same computer from my friends wireless at his house, and from the wireless at work, all from the same computer that will not connect at home. I have also tried different operating system, Ubuntu, and nothing same error message. I have reinstalled the program, and tried other programs,,nothing. I have also deleted that key in the registry, from the check box earlier. At home it does not have that pop up saying " the key is unknown" anymore, even after deleting the key. Yet it does from all the other locations. I do not check it from anywhere else from fear that this will happen everywhere and then I can use it at all. The only difference I can see in these situations is my router, as my friend uses the same ISP, and the same computer was used from each location.