Sorry, this is propably hard to reproduce as it seems project specific, but if you've run into the same kind of problem I would love to get some pointers on what I could do to fix it.
Targeting the webplayer, I'm loading most of my scenes from external files built with BuildPipeline.BuildStreamedSceneAssetBundle. Now, I can load two scenes, and jump between any number of times without problems, but when I try to load a third scene using WWW.LoadFromCacheOrDownload, Unity's plugin just crashes (actually lollypops on Mac) on me. The order at which I load these scenes doesn't matter, it's always the third scene... The player log doesn't help much either, as the last entry is:
starting www download: http://127.0.0.1:8080/game/p-p/Level_3.unity