Error with surf?

Hello !
Well, I did build my first map with some water on it. Added the terrain tag and all, that's okay.
Problem is, when I'm "touching" the water, It asks me if I wanna use surf, and when I do, it crashes with the following message :
http://prntscr.com/jswfwm

I have some questions regarding that.

First : Why does it ask me if I wanna surf? I mean, I didn't touch HMs, nor badge restrictions, and I don't have a pokemon that can use surf in my team.
Second : Which file do I have to edit to fix this bug? I'm not a programmer, and I don't have knowledge, but I can always learn by observing.

Thank you guys ^^

I can tell you something regarding the first question: When you are playing the game from RMXP it is in debug mode and it allows you several features that a normal player wouldn't have when playing your game. One of them is being able to use HMs even if you don't have badges and/or pokémon. In debug mode you can also edit things from the debug menu as well as pass through objects when holding ctrl. It is intended to help testing the game quickly (for example in your case it helped you figure out something went wrong with surf in some modification you did, without you having to go through the whole game and getting surf years later just to figure it out).

I think you should check your terrain tag.

Thanks for the answers ^^
The terrain tags are good, I checked with the tutorial and it's good :o
Thanks for the informations Joltik ! It indeed is good :D Do you know where is the default code for surf?

Hey !
I found the problem ! It was because of an installated plugin, Marin HM moves into item ^^
I removed it and that's okay :)
Thanks for the informations guys I love you :3