"Particle system meshes will only work with exactly one(1) sub mesh"

We have a project with a few prefabs, each containing multiple particle effects.

At some point we started getting the above error both in the editor and on playing (in fact it gets spat out three times on play). Weirdly it happens even on opening a level that doesn’t have any particle effects at all.

Since the message helpfully doesn’t tell you which particle system is broken, I went through and changed every particle mesh renderer I could find to billboard. I applied the prefabs, shut unity and restarted it, but the problem still persists.

Any way to know which prefab is causing this problem, or how to fix it now it’s here?

Changing to billboard wont help you because Shuriken/Unity will keep the setting (the mesh being emitted) in memory regardless if changed to Billboard. You can test this by assigning a Mesh, changing to Billboard and then back to Mesh (it will remember the mesh that was assigned prior to changing to Billboard).

So instead of setting everything from Mesh to Billboard, you have to set Mesh to None and that will solve the problem… well partially because the mesh that is causing the problem still won’t be usable.

You need to check all your meshes and see if they have more than one material. Emitting a mesh that has more than one material is more often than not the cause of this warning message.