It is not a duplicate of #1047, because I am getting different error message. I am using Windows 8.1 Enterprise. It is not a problem if a tex file is saved on a local disk. The problem showes up only if a tex file is saved on network drives (I have tried two).
One workaround is to delete a tex file leaving it open in TeXstudio. Then TeXstudio will inform that file has been deleted on disk asking for restoring it. Choose "Save" and file is saved now.
Could not get write permissions