pokemonfanceetje123 is right, there have been two forums that are currently not accessble anymore.
One of them was "RAM (old)" https://projectpokemon.org/forums/forums/forum/67-ram-old/
The other was "Saves (old)" https://projectpokemon.org/forums/forums/forum/66-saves-old/
Threads in there, like this one https://projectpokemon.org/forums/forums/topic/13556-complete-pokedex-cheat-causes-dream-worldgame-sync-error-code-13204-fix-here/, are still accessible but the forums are not.