Something had to change at BigStock.
I'm on MacOs 10.7 and FTP doesn't work for me when using CyberDuck anymore (last 5 - 7 days). I have installed two days ago FileZilla and it works.
Same with Web Uploader - FireFox doesn't work for me now - week ago it did - I came back to Safari and upload to BS works.
I don't know what's going on - but try FileZilla and Safari - it really works for me.