cannot resume dead coroutine?

20:43:45.702 - ServerScriptService.Script:47: cannot resume dead coroutine 20:43:45.702 - Script 'ServerScriptService.Script', Line 47 20:43:45.703 - Stack End

Why am I getting this error? It seems like I am using a 'dead' coroutine... Can I know why that is happening and how I can get past it?

Thank you.