Battle.net Agent does not have permission to write files to the Battle.net folder. Follow the steps below to resolve the issue.
Run the game in Administrator Mode to address many installation, patching, networking, and start-up errors.
Repair Disk Permissions to resolve any permission conflicts with logon modules.
Reset Folder and File Permissions to make sure there is no conflict between the latest OS update and your permissions.
Try running the game on an administrator account to resolve permissions issues.