In my experience, that 0.8.21 Iannix build runs perfectly on OSX 10.6.7, so there might be something anomalous in your installation.
Did Iannix crash on its very first invocation following your upgrade from 10.5, or were you able to open a score or do some edits before it began crashing on launch? I’m wondering if it is attempting to load a file that is corrupted (sometimes apps in early beta don’t have all the input validation in place, and bad data might cause an out-of-bounds access). To eliminate the possibility of a bad startup file, you might try temporarily relocating your data out of the “Project” subfolder so Iannix will not find anything to open upon launching.
When you upgraded to 10.6, did you do a clean install or an upgrade install? I don’t have any particular issue in mind, but if you did an upgrade, I wonder if some kind of corruption of your app occurred. If you haven’t already done so, it might be worth your time to reinstall Iannix.
Yes, from your stack trace, it does look like it was in a QT call before vectoring through address zero, but 90% of the time an app built on QT will be inside a library call. The invalid access comes out of the Unicode conversion call, and that might be while parsing the name of the default score file. It is unlikely to be a “QT problem”, per sé, because all of the QT runtime support required by Iannix is inside of iannix.app — your QT dev tool installation should have no bearing on this.
I’m trying to run from an install of the latest release, yeah. Not building from source.