What does this error mean?

Invalid pass number (17) for Graphics.Blit. Material=Hidden/Dof/DepthOfFieldHdr, npasses=16
UnityEngine.Graphics:Blit(Texture, RenderTexture, Material, Int32)
UnityStandardAssets.ImageEffects.DepthOfField:OnRenderImage(RenderTexture, RenderTexture) (at Assets/ImageEffects/Scripts/DepthOfField.cs:371)

It means a shader ran too many passes. Looks like the Blit shader, called from DepthOfField.

You’ll need to fix the shaders or the scene to allow it to run in fewer passes.