KDE3.1.2/sid - missing mime types

[Mark Niven]

In order to use KDE3.1.2 I upgraded from sarge to sid....but now KDE has 
become unusable. The KDM sign-in screen appears normally and allows 
log-in, but this is followed by a flurry of error messages: and 
eventually a blank screen rather than the desktop:

Error - KDesktop        Could not start process
                        unable to create io-slave
                        Klauncher said: unknown protocol "file"
Sorry - KDE Panel  could not find mime-type
                        application/octet-stream
                        inode/directory
                        inode/directory-locked
                        inode/blockdevice
                        inode/chardevice
                        inode/socket
                        inode/fifo
                        application/x-shellscript
                        application/x-executable
                        application/x-desktop
Clearing all these messages leaves a blank screen but at least the right 
mouse button does give access to the menu.

Looking at kdm.log gives these error messages:
kdecore (KIconLoader): ERROR: Error: standard icon theme "crystalsvg" 
not found
!
Conflict in /usr/lib/qt3/plugins/imageformats/libqjpeg-non-mt.so:
  Plugin uses single threaded Qt library!
Conflict in /usr/lib/qt3/plugins/imageformats/libqmng-non-mt.so:
  Plugin uses single threaded Qt library!
kdecore (KIconLoader): ERROR: Error: standard icon theme "crystalsvg" 
not found
!
kdecore (KIconLoader): ERROR: Error: standard icon theme "crystalsvg" 
not found
!
Conflict in /usr/lib/qt3/plugins/imageformats/libqjpeg-non-mt.so:
  Plugin uses single threaded Qt library!
Conflict in /usr/lib/qt3/plugins/imageformats/libqmng-non-mt.so:
  Plugin uses single threaded Qt library!
kdecore (KIconLoader): ERROR: Error: standard icon theme "crystalsvg" 
not found
!

According to dselect I have the latest versions of all the packages 
installed (kde-core with some additions).

X itself seems to be working if I don't try to use KDE - I am currently 
using Mozilla with Windowmaker.

It seems to me that some essential KDE configuration has got left out 
and I would be grateful for help in putting things back together.

Mark