If you are getting this error when running Unity Engine in game mode:
rect == rt->GetGLWidth() rect == rt->GetGLHeight()
It’s actually an error emitted by the editor itself, nothing to worry about. To remove this issue, go to Window → Layouts → Default to reset the editor layout. The error will then disappear.
The error is usually associated to conflicts between image effects and screen aspect ratio. It’s not really a serious issue, just follow the steps above and you’re good to go.