There is more than one Light Select render element that includes the same light source

There is more than one Light Select render element that includes light object [object]/environment lighting/sunlight. LightMix result might come out too bright because of this. The render elements are [list]

This message appears if a single light (light object, mesh with Corona Light mtl, environment light, or sunlight) is assigned to multiple CShading_LightSelect render elements at the same time.

Assigning a light to a LightSelect render element is required to make it possible to adjust that light's intensity and color using the LightMix tool. Having some lights in scene which are not assigned to any LightSelect element is not an error - in such case the rendered image will come out correct, although it will not be possible to alter those unassigned lights in LightMix. But if a light is duplicated (assigned to more than one LightSelect element at the same time), then it results in incorrect (too bright) LightMix output.

Solutions:

Either:

• Use "Setup LightMix Elements" button in Render Setup > Scene> Setup Lightmix to automatically create LightMix elements based on all scene light groups (this will automatically get rid of any duplicates)
  
  
  
  "Setup LightMix" button
  
  

Or:

• Make sure that each light is assigned to one CShading_LightSelect element only by reviewing them manually in Render Elements list

Example:

Removing the "Wall light 4 (duplicate)" LightSelect element fixes the issue and now all of the lights have the same intensity: