When trying to open an Office 365 site in SharePoint Designer 2013 you may encounter the following error:
“We are unable to connect right now. Please check your network settings and try again later”

Perform the following steps to fix:

  1. On the local computer, browse to the following folder:
    C:Users<username>AppDataRoamingMicrosoftSharePoint DesignerProxyAssemblyCache
  2. Delete all files and folders in this directory.
  3. On the local computer, browse to the following folder:
    C:Users<username>AppDataRoamingMicrosoftWeb Server ExtensionsCache
  4. Delete all files in this directory
  5. Try opening the site in SharePoint Designer again. It should work.