Windows 10 version 1903, May 2019 Update, is currently available for any device enrolled in the Release Preview ring of the Windows Insider Program and for MSDN subscribers, and it appears that no everyone will have a smooth upgrade.
If an external storage is attached to the device during an in-place upgrade using the Windows 10 May 2019 Update ISO file or through Windows Update, you’ll get the “This PC can’t be upgraded to Windows 10” message.
Microsoft explains that the reason for blocking the new feature update is because of “inappropriate drive reassignment” on computers that have an external USB device or SD memory card attached.
Windows 10 upgrade workaround
To resolve this issue, the company recommends users to remove any external media attached to the device and then restart the installation of the Windows 10 May 2019 Update.
In addition, you also want to disconnect any unnecessary peripheral before an upgrade, you only need a keyboard, mouse, monitor, and internet connection. Furthermore, it’s a good idea to uninstall any apps and drivers that may conflict with the upgrade, after the installation, you can always reconnect the peripherals and reinstall applications again. (You can follow these additional tips to avoid this and other problems upgrading to Windows 10 version 1903.)