Hallo Thomas,
I just tested in my 7.40 system (running kernel 7.42 pl 414) and appending the URL with $~transaction=FF.6 brought me a selection screen:
It seems that the issue you are facing is not related to the transaction itself, but maybe with other part...
Please share the kernel version and patch level used in your system and the SAP_BASIS version and support package level.
Are you calling the transaction via WEBGUI service or maybe using a Portal (transaction iView)?
Thanks and kind regards,
Cris