Can't Bitlocker encrypt second drive

I successfully encrypted my OS-drive with Bitlocker with the "password on startup required" options in the GPO.

Now I want to encrypt my second USB-based HDD. Windows 10 recognizes the drive as a regular drive, not as an usb-drive. When I want to activate bitlocker it simply says that there is a conflict with the GPO start options of bitlocker and the error code 0x8031005b

Any ideas on how I can get my drive bitlocked? Thanks in advance.