At the top of the script where it says AUTOSCROLL_MAP, you put in the Map ID where the panorama is used and the x/y movement speeds. There's an example already there.
There isn't one built into RMXP (although there was for it's predecessor...) so you'll need a script. I used this one in Attack On The Space Station for the scrolling space background. Make sure you credit The Sleeping Leonhart...
Trial 1: City
Map Name: Nerium City
Map:
Critique Requested: Yes
Credits: Spherical Ice and Alistair for tiles
Notes: Nerium City, is home to the region's Poison type gym and Experimental Potion Laboratory. The city sits high up on a cliff that looms over the sea. To the north, lies a forest...
It says the problem right there, you're missing the image trainerNearby from the pictures folder. Also I don't think this is the place to ask for error help
Map Name: Jubilation Town
Trial: Trial #5, Celebration
Map:
Critique Requested: Yes
Credits: Spherical Ice for tiles and over-worlds.
Notes: What an occasion! It's all smiles in Jubilation Town as they celebrate Victor's 30th year as the Gym Leader. Visitors and past challengers have come from...
Pokémon Police Force
This is a game I worked on for Relic Castle's very first Game Jam but I missed the deadline due to being busy around the last few days. I then decided to continue the game into something bigger but that didn't last long. I hadn't uploaded this game to the new RC so I...
The evolution stones are given to you by a scientist on the 4th floor but to get there you need to take the left-most teleport on the 3rd floor. I think I changed Graveler evolution to level up, maybe at level 40? If not you may be stuck with a Graveler...