"Could not find main method from given launch configuration" when using Java+Scala+Slick2D

Okay, I got it to work. Apparently, all I needed to do was restart eclipse. And then magically, it started detecting the Main class:

But the jar started giving me noClassDefFound errors for the Slick2d, LWJGL and other libraries. That's where JarSplice came to my rescue. I exported the project as before, with all the libraries and resources.

Then, I fired up JarSplice and added everything as follows:

1. Go to "Add Jars" and add the project.jar just created through eclipse, add lwjgl.jar, slick.jar and scala-library.jar. lwjgl and slick should be in your project lib folder where you would have imported them. scala-library should be available wherever it says it is. Make sure you add that as well
2. Next, when I tried to "Add Natives" it kept giving me "Duplicate library" error. So I removed them all and kept it empty.
3. Next in "Main Class", I entered the path to the main class i.e. game.TicTacGame
4. Finally, "Create Fat Jar". And it works perfectly :)

I just encountered the same problem, and here is how I solved it:

1. Open "Run As" --> "Run Configuration" on the project you want to export

2. Click "Search" for Eclipse to refresh the list of main class

3. Then export Runnable JAR file again, and everything goes smoothly.