Ensure you are using BS Tweaker 5.x for BlueStacks 4. If you have moved to BlueStacks 5, you should look for BS Tweaker 6. Final Verdict

Only download BS Tweaker from the official website (bstweaker.tk) or trusted community forums like XDA Developers.

Ensure BlueStacks is completely shut down. Use the "Full Stop" button in the BS Tweaker Main tab.