To be boring - but Ditto I have a reasonably complex scene - try and switch the object to static and then crashes at 5/11 Clustering | 62 Jobs. In fact makes my entire computer unresponsive so have to cold boot. Unity 5.1

JPV1234 Thank you, that solved ours

'changing the Indirect Resolution in Baked GI. Before I was at 2 texels per unit and Unity was stuck at clustering. However when I changed that value to 1 it worked like kind of magic. The baking was strange since the scene was darker than expected, but it worked finally.'

Unity 5.0.2p3 Is still seeing this issue.

Nice work unity developers i ave pay month Subscription for not build my project.This work for me,in lighting wondow go to object and set advanced parameters to defaul very low resolution and unity5 buil bake.This my request for unity developers FIX THIS BUG AND GIVE ME ONE MONT FREE LICENSE TKS BECAUSE I DONT PAY FOR BUGGED ENGINE!!!!!!!!!!

Guys I think I solved it. If you don't want necessarily to have Baked lighting, this problem is gone. First, make sure all your lights' baking are set to Realtime. THEN, VERY IMPORTANT, THIS IS WHY THE BUG WAS PRESENT: DON'T CHECK ANYTHING AS 'STATIC'. So, no STATIC, no BAKED = no STUCK CLUSTERING / LIGHT TRANSPORT. Hope it helps!

Still seeing this on 5.0.1f1, stuck at 5/11 with a low poly scene of total 11.2k tris and 24.8k verts.... annoying...

This is really frustrating :(

I found this thread searching for the same answers when I figured out just now that if you want a large we'll say as in my case .. terrain like 5000, 5000, start with the default size of your mesh or a smaller version and incrementally add more to it. It seems to process more easily due to only having to process the added content.

Light transform was where it was happening to me also and this will stop you from testing .exe of app because .exe process tries to copy a file that is still being used by another process. .... The stuck light transform job (10 for me) that appears to just do nothing as someone here stated, still has a handle on the file apparently and it will keep you from creating a .exe file of your app. Hope this helps someone. I have done just what I am saying and now my map is almost the size I want with no issues. All jobs completing fine.

Unity does not like to work on large jobs apparently... ;)

NIGHTCODER99 have 100% right, it seems that Enlighten precompute (clustering) has a problem with big meshes, "BIG" means not in terms of vertices or faces but their scale.

Steps to reproduce:
You can freeze GI simply putting one plane on the scene (even Plane object from Unity) and scaling it 16 times (16,16,16). Now try to build GI lighting (even without baking textures - only realtime), job freezes at clustering.

Workaround:
Instead of using one plane 16x16 try to create more planes but smaller in dimensions, the problems solves immediately. For example 16 planes scaled twice time (2x2).

just check the meshes you are using. for me i was using a mesh for my floor and i was scalling it to 20 units . i deleted and duplicate it 20 times and used it worked.