hmm i'm stumped. the version of pyqt being used in libprs500 is obviously linked to a pre 4.3.0 qt. I don't see how though. try checking out libprs500 svn
https://libprs500.kovidgoyal.net/wiki/Development
(delete the libprs500 .egg file from /usr/lib/python2.5/site-packages first)