centos 6.4 x64 can not login to kde, Could not start D-Bus. Can you Call qdbus?

hello all, just did an upgrade from 6.3. to 6.4, i found that i can not log
into kde.
after selecting kde at login screen, it shows an ugly window saying
Could not start D-Bus. Can you Call qdbus?
and only one ok button, if i click it, it returns to login screen.

gnome desktop is fine though.

how can i fix it ? thanks !

the error is :

startkde: Starting up...
/usr/bin/startkde: line 283: 12207 Segmentation fault (core dumped) qdbus >
/dev/null 2> /dev/null
startkde: Could not start D-Bus. Can you call qdbus?
Warning: Missing charsets in String to FontSet conversion
Warning: Unable to load any usable fontset

already tried:
reinstall  "X Window System"
yum install qt qt-demos qt-designer qt4 qt4-designer PyQt4

and

export QTDIR=/usr/lib/qt4
export PATH=$QTDIR/bin:$PATH

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