This week's book giveaway is in the OCAJP 8 forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide and have Edward Finegan & Robert Liguori on-line! See this thread for details.
Presumably C:\Two already exists (perhaps it's actually the directory you wanted to move the file to), so you can't rename C:\One\sai.txt to that. Did you actually want to rename it to C:\Two\sai.txt? If so then do that.