can´t activate Pianoteq V5.8 ( V7 is on 3 computers /bought as V5 )

Hi,

i just installed the new 7.4, ......i own PT pro. Its activated on 3 computers.
but also wanted to install finally the old V5.8 on my new computer, since i like the old Blüthner better.
and, since its sometimes handy to be able to start two pianoteq (standalone) instances in parallel.

i run the old V5.8 on my old computer.,
i bought PT when it was V5

whats the trick ?