It could be that the file is opened by another program somehow. That would give the error you described. I know that for torrents, it won't let you modify anything you are torrenting. If a metro app is still considered as running and has a file handle open, it won't let you modify it.
I have this issue even with the Windows 10 TP , damn it. Takes me about a minute to wait and keep clicking "Try Again"... Maybe I should get a Mac?