There is a new restriction that is active in some E38 controllers and possibly other models as well but so far we've only seen it in E38 controllers.
It prevents you from changing the VIN to any other value.

To bypass the restriction we've found this procedure to work:

1. Connect up the ECM (i.e. vehicle) to FlashScan and FlashScan to the PC as you would normally.
2. Start the V7.5 Tuning Tool software.
3. Start reading the contents of the controller.
4. Once the software has started reading the controller, click [Stop].
5. Click [ok] to the "Data transfer was interrupted" message.
6. Do NOT switch off the ignition.
7. Wait for the countdown to complete and close the window.
8. Open the Security window and click on the [Check Status] button.
9. Wait for the check status to complete, then goto the VIN window and change the VIN - it should work.
10. Now switch off the ignition and wait for the countdown to complete (I would prefer if you waited 30 seconds instead of 15).
11. Switch on ignition and the VIN should now be the new VIN.

Regards
Paul