PoP Backlogging - 7th Trial issue

[amandabatts]

Hello,
I'm taking a trip down memory lane and working through the Planes of Power using EQProgression's guide. I'm currently in the Plane of Justice but can't get the Tribunal to spawn for the final encounter. I've hailed one of the Tribunal NPCs, have the Mark of Justice on my cursor, and have entered the area with the red portals after hitting "U." However, the final boss isn't appearing. I’m zoning in with just myself and a healer merc. What could I be doing wrong?

Thanks in advance!