Microsoft blocks Windows 10 May 2019 update for PCs with USB storage or SD cards attached

If you have a PC running Windows 10 with the April 2018 Update (version 1803) or the October 2018 Update (version 1809), you won't be able to get the latest version of Windows unless you remove all attached USB storage devices and SD cards. Disconnect any external media, restart the May 2019 update and you're good to go.