Phone [Q] [Help] Sony ABD Interface overwrites Sony Fastboot Interface

Hello!
I have a problem, I wanted to flash my phone, but now there is a little fail which i am trying to find a solution for several hours for.
I installed everything I need, Flashtool and the drivers, but now since when I want to enter Fastboot with the flashtool, it needs a interface (Driver needed for this I guess: Sony Fastboot Interface).
But everytime I want to make the Android Device in the Device Manager (I hope its called like that) to the Sony Fastboot Interface, it changes back to Sony ADB Interface, but I need the Sony Fastboot interface.

What am I doing wrong? Could you help me?


Thanks in advance guys....
If you need any further Information just ask...

Thanks...