I'm not sure the device in use problem is kp48 related. Last time I experienced this problem I had a queen beecon accessing images in MyDocs.. When you connect by usb make sure there are no open programs running (like filebox) which may be accessing MyDocs. Try connecting immediately after rebooting the phone as the desktop loads. The only other way to access your system reliably is to install OpenSSH-server from the repository, and connect to it wirelessly using WinSCP.