185.18.08 is a beta and my kubuntu is not tweaked, so I assume this error is already known, but just for the case:
kdm (the X session manager) is running, but fails to spawn kde (the window manager). Excerpts from the relevant logs:
xsession-errors:
kdeinit4: Fatal IO error: client killed
kdeinit4: sending SIGHUP to children.
klauncher: Exiting on signal 1
kdeinit4: sending SIGTERM to children.
kdeinit4: Exit.
KCrash: Application ‘ksmserver’ crashing…
Warning: connect() failed: : No such file or directory
KCrash cannot reach kdeinit, launching directly.
Unexpected response from KInit (response = 0).
startkde: Could not start ksmserver. Check your installation.
kwin: Fatal IO error: client killed
Qt-subapplication: Fatal IO error: client killed
kded4: Fatal IO error: client killed
kdm.log:
X.Org X Server 1.6.0
Release Date: 2009-2-25
…
Current Operating System: Linux roland 2.6.28-11-generic #42-Ubuntu SMP Fri Apr 17 01:58:03 UTC 2009 x86_64
…
*** glibc detected *** /usr/bin/X: double free or corruption (fasttop): 0x0000000002a2a270 ***
======= Backtrace: =========
/lib/libc.so.6[0x7f0ee5ee2cb8]
/lib/libc.so.6(cfree+0x76)[0x7f0ee5ee5276]
/usr/lib/xorg/modules/drivers//nvidia_drv.so(_nv001540X+0x8d)[0x7f0ee292ad5d]
/usr/lib/xorg/modules/drivers//nvidia_drv.so(_nv001410X+0x86)[0x7f0ee2938356]
/usr/lib/xorg/modules/drivers//nvidia_drv.so(_nv001339X+0x5a)[0x7f0ee292baba]
/usr/lib/xorg/modules/drivers//nvidia_drv.so(_nv001403X+0xa3)[0x7f0ee2938163]
/usr/lib/xorg/modules/drivers//nvidia_drv.so(_nv001410X+0x10a)[0x7f0ee29383da]
/usr/lib/xorg/modules/drivers//nvidia_drv.so(_nv001339X+0x5a)[0x7f0ee292baba]
/usr/lib/xorg/modules/drivers//nvidia_drv.so[0x7f0ee2ba17b8]
/usr/bin/X[0x5370f8]
/usr/bin/X[0x50170e]
/usr/bin/X(BlockHandler+0x50)[0x451d20]
/usr/bin/X(WaitForSomething+0x161)[0x4ef561]
/usr/bin/X(Dispatch+0x80)[0x44e020]
/usr/bin/X(main+0x3bd)[0x433d8d]
/lib/libc.so.6(__libc_start_main+0xe6)[0x7f0ee5e895a6]
/usr/bin/X[0x433219]