Rename error due to read-only?

I've had plenty of times I try to let ReSharper rename something only to be greeted with a message "Failed to modify file", and no changes.  This is irritating, but spuratic, so I've never really been able to understand anything more than that about the problem.

However, today, I am getting the following error dialog while trying to rename a variable:


I don't know what this means, as I've been editing these two files for the last 20 minutes or so.  They are NOT marked as read-only.

Any ideas on what is going on?  Has anyone else encountered similar issues?  Any work arounds?

Thanks,
Eric

P.S. - I have ReSharper 8.2.3