Same thing for me here. I had a hard time with the AU version. It validated fine, but Logic would crash almost every time I opened an instance of Nebula. I had to go back to using the wrapped VST, which is working great (except I can't insert it on a mono track for some reason).
By the way, Nebula sounds great and is doing wonderful things for my mixes!! I am happy.
Just installed the AU-version, validates fine, but only stereo/mono-stereo is available. No crashing as of yet. I only hope that the latency and mono will be fixed. @ Giancarlo: which version of OS and Logic are you using? Maybe an update will resolve things?
Give this beta a little bit of patience, I've been able to complete three productions (though very buggy, and sometimes pretty crash prone). Been reporting many numerous crash reports with various uses within Logic to Gian over the past couple of weeks for all of us to get things stable on a day to day production basis.
Case in point it crashed 30 differnt times last night and sent Gian four unique crash reports telling him exactly how things crashed and why in Logic. I'm glad the AU is at least released in a beta fashion so we can iron this out. DOn't forget to send him your crash reports and general usage!!