Transfer problems - 0 bytes?

Hi, thanks in advance to anyone who can offer urgent help. I have been using the ftp trial version and have been delighted. I bought a subscription key today, because the trial expired, and everytime i try and drag a file accross to go on my server, the file updates, but it is shown as having "0 bytes" and doesn't contain any data!

I really need help and advice on this as soon as possible, thank you so much if you can help.