The process for the mtp protocol died unexpectedly when mounting Android devices

I have a problem with mounting my phone (Android 4.4.2) and tablet (Android 4.2.2) via USB. Often I had an error "The process for the mtp protocol died unexpectedly" when trying to open them using KDE's file manager Dolphin. Sometimes there are no error messages but connection is very slow -- it may take about a couple of minutes just to open any folder and it is impossible to copy anything from them for example. Slackware is 14.1 stable. There were no problems with USB and Android devices when I used Fedora. How can I solve it?

Sorry for my English.