It looks like another plugin that connects the launching action's activated() signal to its installed gui elements.
That signal is no longer supported under Qt 4.8, which is what QGIS 1.7.4 is built against/bundled with on Mac OS X. I have seen this problem with other plugins (now both C++ and Python).
I have not tested this, but changing the signal to 'triggered()' in the noted file might fix the problem. You can test it with re-compiling the latest master branch (1.8 RC 1, not 1.9 right now, as it is readying for release).
(I have added this to Simbamangu's bug report. Can someone compile and test fix? I won't be able to for a couple of days.)