TypeError Cannot read property 'get' of undefined

[ls9405]

So, this is my first bug report. I just added a quest system plugin (game_stailer94's quest plugin) and the Yanfly main menu manager plugin. So, I added a few quests using the quest system plugin and I wanted to test them out. I loaded up a new game, but once it loaded, I couldn't move. Pressing escape did nothing, clicking on the screen did nothing, it was completely unresponsive. Then, I loaded a save file that was in a city. I left the city, and then a TypeError occured. Every time I go to the world map from a location, the same thing happens. When you start a new game, the player's starting position is on the world map, but the typeerror doesn't occur, it's the one I mentioned before. I honestly have no idea how to recreate this error.
Here's some screenshots that might reveal what the problem is. Please help, and thank you in advance. If anything else is needed (like more screenshots of things), be sure to ask as I will do exactly what is needed.

 

[Andar]

You already found the cause of the error: you loaded an old savefiles after installing a complex plugin.
Adding a plugin almost always makes older savegames incompatible, with exactly those undefined errors as a result. Only minor Plugins might be able to handle older savefiles, but nothing like a quest plugin that needs its own data structure in the saves.

You have to start a new game with the quest plugin, and if that has problems then follow those bugs but never errors from then incompatible old saves.

 

[ls9405]

@Andar Thanks, that fixed the TypeError problem, but I found out what the problem with not being able to move was myself (it was a broken autorun event). Thanks for the help! I hope the rest of the community is as nice and helpful as you were.