From Glitch City Laboratories
A player has activated the "Object Event" message by speaking to a Pokémon whom cannot usually be spoken to.
The term "Object event." refers to an error trap in Pokémon Gold, Pokémon Silver, and Pokémon Crystal. The message will be displayed when the player attempts to speak with a non-playable character whom through usual gameplay cannot be directly spoken to and is part of either an event or 'cutscene' such as Lance in the Hall of Fame room. This message exists for unknown reasons, however it may have been placed in the games to inform the developers of such 'special' NPCs for example, when the player speaks to characters with no dialog assigned to them, or to prevent any possible game freeze.