Hi @Keyplayer,
is this Nuendo 12, and do you still have an USB eLicenser with the former version’s license?
If so, you could perhaps temporarily install the former version to a separate folder (or better: on a second PC) and open your project there, and then remove / replace that Prologue entry by something that would work in N12.
Besides, last year Steinberg did indeed remove a few things when stepping up from Cubase / Nuendo 11 to the current version(s) 12:
Best,
Markus