][1]I have a SM model that works fine with 4.4 but fails to load at about 25% in 4.5. It totally freezes the editor with the only option to force quite from task manager. I’ve tried importing without textures and materials but get same result. I’ve also tried reducing the model pollycount but this hasn’t helped.
Have you already created a lightmap UV channel on this model ? Its seems there is a bug when the “Generate lightmaps UV” is tick on when you try to import a mesh whit lightmap UV already set. So far its been the only time i have seen a crash on import, might want to check it out. 
Hope it help !
P_A
Ah yes well I was playing around with the light map options and everything did get a bit crazy. I’ll check and report back, cheers !
Ok the problem is defiantly to do with generating UV lightmaps as when I import without that checks it imports fine. The thing is I haven’t already generated a lightmap channel as far as i’m aware ?
Hummm maybe an issue with the channels. What 3D package are you using and many channels your mesh have ?
Fixed it ! I basically had some messed up UV’s on the part that wasn’t importing. Remapped them and all is gravy
I fixed the issue, it was due to a bad uv map that was ignored in 4.4 but 4.5 didn’t like it. Obviously it shouldn’t hang and freeze like it does but at least I found the issue.
Mr Sulky has the correct answer. I think there is a bug here because I had this issue but was able to succesfully import the FBX model by unticking “Generate lightmaps UV” in the FBX import options.
I think both answers are correct but the bigger issue is the bug for sure.