Not always unsafely removal of usb drives causing the problem, there may be another problem related to Windows driver or similar to that which causes a device not recognized issue. So, we have to identify the problem for getting such an error and try to fix them manually step-by-step to troubleshoot the issue. Actually, there is no exact or specific reason for getting this error message. No matter what Windows OS version (it might be Windows Xp, Windows Vista, Windows 7, Windows 8, Windows 8.1 or Windows 10) you are using, you certainly get the usb not recognized error more than once in your lifetime while inserting USB flash drive or any external USB drive in your PC.

The error is very common and has been discussing all over the web portal, forums over the years.