Plasma Desktop - An internal system error has occurred.

[Peter G.]

My system is up-to-date every day. Yesterday, right 
after logging in and again today, right after logging 
in, the following pop-up appeared on the screen, before 
I did anything:

A problem that we were not expecting has occurred. 
Please report this bug with the error description.

Details:

Did not receive a reply. Possible causes include: The 
remote application did not send  reply, the message bus 
security policy blocked the reply, the reply timeout 
expired, or the network connection was broken.

When this occurs, I am unable to do anything: no right 
click on the desktop, the task bar is inactive and 
unresponsive, but I can still use the active screen 
edges to change virtual desktops. I click around, 
repeatedly clicking on the application tabs on the task 
bar, click the fedora 'f' a number of times, and 
presto! Suddenly it all works again. I don't notice any 
problems with the session until, presumably, the same 
error upon the subsequent login.

Wha?