Today, all my FTP connections have suddenly stopped working. I thought it was a problem with FileZilla, but have since tried 4 or 5 different FTP clients and none of them will connect to anything. Sometimes the connection just times out, and other times it goes through all the authentication and login seemingly successfully before the message appears: 'Critical error: Could not connect to server' I'm using a 2011 MacBook Pro, upgraded to Yosemite about a month ago (and have been using FileZilla on a daily basis since), but otherwise I can think of no hardware or software updates that have been made. I've tried restarting my router and my computer. I've also checked the Mac firewall, which was already switched off. After googling the issue, I read that turning off 'passive mode' might fix it, but it doesn't. I haven't a clue how to go about fixing this problem! Any ideas?