"Error: Could not find or load main class net.minecraft.client.main.Main"

This issue has started from around 5 days ago till today. it occurs only when i open my launcher and press play. after pressing play, it immediately brings me back to the Game Output of the launcher and says "Error: Could not find or load main class net.minecraft.client.main.Main" and doesn't open Minecraft. please give me an easy and fast fix that can solve this this issue!