PS3 CFW 4.86 CEX - Won't connect to FTP server (Connection closed by server)

Hi, I've had this CFW PS3 for about a week now and have been using FileZilla FTP to transfer files back and forth from my PC to PS3 without any problem.
I was in the middle of transferring a PS2 ISO to my HDD and all of a sudden I get this message:
Image may be NSFW.
Clik here to view.
As I said, it's been working perfectly without any problems, I haven't changed any settings on my PS3 and nothing on my PC
and now it connects to the PS3 for around 20 seconds...

PS3 CFW 4.86 CEX - Won't connect to FTP server (Connection closed by server)