I stumbled over the same problem. plasmoidviewer gives a bit more information:
findServiceByDesktopPath: not found
Traceback (most recent call last):
File "/usr/share/kde4/apps/plasma_scriptengine_python/pyappletscript.py",
line 19, in <module>
from PyQt4.QtCore import *
ImportError: /usr/lib/pymodules/python2.5/PyQt4/QtCore.so: undefined symbol:
PyProperty_Type