To fix Roblox start error, you need to Reset your Router, Reset the TCP-IP with Nesh, Disable proxy settings, Turn off antivirus Software, Allow Roblox through Firewall or Reinstall Roblox.

Fix #3: Update Roblox installation files. If Roblox is still showing the same crash error, the final solution that you can try is to update certain files in the installation folder.