Because of ongoing issues related to Windows Mobile Device Center, we do no longer support the connection between the Smart 3 and a computer.
Please use the alternative method (export to USB stick using Mind Express on your PC) as described here.
An alternative method is available since Mind Express v22.214.171.1244.
It doesn’t require a connection to a computer to export data to the Smart, it only requires a USB stick:
Update Mind Express on your computer to v126.96.36.1994 or higher. Choose ‘File’ > ‘Export to USB stick for Smart3’ in the menu to export to a USB drive. When finished, connect the USB drive to the Smart (using the USB OTG adapter cable) and your Smart3 will automatically start importing the files from your USB drive. Follow the onscreen instructions. When finished, the device will reboot and you will be able to open the file you have imported.