we would like to examine the scene file and fix the issue if you are able to send it to us, but to work around the issue, you might have luck if you go to system preferences->general, and check the box for "close windows when quitting an application". This ensures that opened docs are not reopened when the app is opened.
Alternatively, we only attach or plugin to the most recently opened model, so you may have luck opening another su file by double clicking it. The problematic scene file should still load, but we won't attach to it, process it, etc. You should then be able to close it without an issue.
We have resolved some issues that would cause complex/large scenes to crash in this manner on OSX in a nightly build. If you are interested in testing your issue out in one of those builds, send me a PM.
