Q:

Why Dolphin refuses to start in Kubuntu 15.10? 

Somehow since updating Kubuntu to version 15.10 the Dolphin filemanager refuses to start by clicking on the icon.  It appears to start as shown by the 'dancing' icon but then does not show up. 
However it can be started by typing the command: dolphin in the Konsole.  Then at first it shows an empty screen and the error message The file or the folder file:/home/user does not exist where user is my username and I've translated this text from Dutch, so the English version might be a bit different. 
When pressing the enter key the text in the addressbar file:/home/user is replaced by /home/user which is the correct folder and then I can see my files. 
Kubuntu is fully updated. 

A:

Finally solved the problem.  The command to invoke Dolphin reads dolphin %i -caption "%c" %u while it apparently is supposed to be dolphin %u. After this correction Dolphin starts immediately.