This is a common issue with Mi 5 phones flashed with the earlier MIUI Global ROM.
In order to Officially unlock, some customers experienced failures attempting to unlock or flash new ROM. To fix this issue please follow the recommended steps below:
1. Download the latest FASTBOOT DEVELOPER ROM for MIUI (Mi 5) here; http://bigota.d.miui.com/6.5.19/gemini_images_6.5.19_20160509.0000.21_6.0_cn_2332931a73.tgz
2. After downloading the file, unzip the contents e.g. mi5_rom folder on your PC. Make sure the images folder and all scripts are copied to this folder you have created. Copy all the content of the zip is easiest way.
3. Ensure your phone is currently powered off at this stage until Step 11.
4. Download Mi Flash 64 Bit from here: http://en.miui.com/thread-272376-1-1.html
5. Follow the setup instructions of Mi Flash once opened, IMPORTANT NOTE: Run as Administrator to avoid issues.
6. During the installation process several boxes will appear with RED Warnings, Agree to install the driver (I) - DO NOT say no to these prompts, the drivers installed effect ADB, FASTBOOT and EDL modes.
7. Download a working copy of ADB / Fastboot Tools from here: https://androidmtk.com/download-minimal-adb-and-fastboot-tool
8. Once Mi Flash is successfully installed you can proceed to start your Mi 5 in Fastboot mode (Ensure you have the files from step 7 before continuing).
9. Open a command (MS DOS) window, go to the start menu (Windows icon) on your desktop and type: cmd
10. In the command prompt change the directory to your ADB directory, e.g. c:\adb_tools
11. Then on your Mi 5 press the VOLUME DOWN and POWER KEY together at the same time until you see the words FASTBOOT and an illustration with an Android and Mitu.
12. In the command window ensure that the device is visible by typing the following command: fastboot devices
13. If successful you will see a short alphanumeric code and the words 'fastboot' to the right. If not you will need to consult our support team or repeat the install of Mi Flash allowing for all drivers to be installed.
14. Now you can put the Mi 5 into EDL mode to begin the flashing process. To do this type the following command in the command window: fastboot oem edl (Note: Mi 5 Screen will at this point go black do not panic this is normal).
15. Now go back to Mi Flash and press the 'Refresh' Button, if successful you will see a device listed such as COM10 or COM20 depending on the USB port or devices already connected via USB to your PC.
16. With the COM device displayed now just browse to the ROM folder you made earlier in Step 2, in Mi Flash press the 'Browse' button and navigate to the Mi 5 Fastboot ROM folder (Step 2). Once selected you can press the 'Flash' button. Wait patiently for this process to complete otherwise you may damage your Mi 5 beyond self repair. Process generally takes about 2 to 3 minutes depending on your PC CPU.
17. Once successfully flashed you can then follow the guide here at xiaomi.eu; https://xiaomi.eu/community/threads/xiaomi-eu-multilang-rom-for-xiaomi-mi5-unlocked-bl-only-released.31231/
Other notes: Customers wishing to use EDL mode without unlock, they need to put a ROM older than 6.5.5 Developer Edition on the Mi 5. However, we recommend to follow the guide above to get up and running with the latest MIUI Global ROM with official support.
Customers are at all times responsible for the proper flashing and installation of all Software. These guides are informational and are accurate as best as they can be provided. iBuygou accepts no liability for the failed or improper flashing of any product which results in dead, brick or other failure of device. Customers must accept all responsibility when performing these operations. If you are unsure please consult with our Technical After Sales Team.