I had that same problem with that Lance fella. After he gave me Clamperl his textures kinda messed up, and he looked like nurse Joy. So i walked in a house that leads to tunnel and everything was fine then.
Also i can't get inside Ghost Tower in Lavender Town. I got Silph Scope for Team Rocket base at Game Corner. At first i thought that Kecleon is blocking the way, you know like in RSE games but i tried to talk nothing happens. I need to go inside Ghost Tower so Mr. Fuji can give me PokeFlute to awaken Snorlax.