Permission errors in PowerShell

Question

I am new to PowerShell. When trying to write a simple script that deletes the contents of a folder and then fills it with files copied from a different folder, I always get

Answer 1

In addition to reasons mentioned in the above posts, i've observed that "Access Denied" error is thrown when the file is being accessed by a separate process (In my case, i had to stop the server before Rename-Item could be run successfully).