This project is from an old version of RPG Maker and cannot be loaded

When you open RPG Maker XP, you might see this message:

Error message when opening a projet from wrong RMXP version
Error message preventing you from opening your project with the current version of RPG Maker XP

Don't worry, it's nothing that bad, this can be easilly fixed!

First of all, you need to know what your RPG Maker XP version is. To do so, open RPG Maker XP without opening a project. You should see that screen:

RPG Maker XP window without project
RPG Maker XP when no project is loaded

You need to click on Help and then About...

This will show a window containing "RPGXP Version X.0Yz"

About window of RPG Maker XP
Window containing the version of RPG Maker XP you are using

In this example it says we're using RPGXP 1.05a. With that information we can fix the project file.

Open Notepad and then open the file Game.rxproj located in your game folder, you should see a simple text:

Project file opened in Notepad
Text written inside the project file

In that text you want the number to match with the number you see in RPG Maker XP about section. In that file it's written 1.06 and your RPG Maker XP is version 1.05a so you will change 1.06 to 1.05

Project file with correct version
Project file with the right RPG Maker XP Version

Once done, you can save the file and open the project with RPG Maker XP again, this should work!