Yakuake failure

After a reboot today in Ubuntu on the Mac, Yakuake 2.8.1 failed to start without giving any error message. However, trying to start it from a terminal gave this:

DCOPClient::attachInternal. Attach failed Could not open network socket
DCOPClient::attachInternal. Attach failed Could not open network socket
---------------------------------
It looks like dcopserver is already running. If you are sure
that it is not already running, remove /home/paul/.DCOPserver_ubuntu-mac__0
and start dcopserver again.
---------------------------------

DCOPClient::attachInternal. Attach failed Could not open network socket
DCOPClient::attachInternal. Attach failed Could not open network socket
WARNING: DCOP communication problem!
kdeinit: Communication error with launcher. Exiting!
DCOPClient::attachInternal. Attach failed Could not open network socket
DCOPClient::attachInternal. Attach failed Could not open network socket
ERROR: KUniqueApplication: Can't setup DCOP communication.

So as suggested I just did (in ~) in a terminal:

rm .DCOPserver_ubuntu-mac__0

Now Yakuake restarted as normal.
I have seen this error before but have no idea what causes it. Happily, it's easy to rectify.