I am having the same issue as others in not being able to upload my site using the latest build in Muse CC. Access to the FTP works fine with FileZilla, but I need to get this to work so my client will have access. I'm using FTP (not SFTP) for the uploaders and it all works fine. What am I doing wrong? I've tried everything!!
There can be something either at your host end or your system.
Most of the times it is a firewall blocking or sudden change in host protocols.
Below two threads may shed some light on your issue-
Hope this helps.