Kept playing around with this one today as I felt it must be something with my configuration and not geany as otherwise it would have already been discovered and fixed. Re-installed all gtk2 related packages - the '-dev' versions as well. Did a 'make clean' and then ran the autogen.sh again. Then did the usual make/make install and this time geany started up as expected ! No real idea what was wrong but I do thank all that read and contributed to this issue. I did note that if you use the '--enable-binrelocs' option to autogen.sh then geany will not start up - so maybe that is how the debian package was built and why that one does not run. Closing this as resolved.