"Could not find the main class" error when running jar exported by Eclipse

I have a java project that works perfectly fine when running it from within Eclipse. When I try to export it to either a `"JAR file"` or `"Runnable JAR file"` the .jar file is created, but when I double click on it to try to run the program it gives me an error that says ``` "Could not find the main class: package.MainClassName. Program will exit." ``` As I mentioned, I tried exporting to both JAR options, I specified the correct class that the main method is in, and when I look through the actual files in the `.jar` file everything seems to be in order -- the manifest looks something like: ``` Manifest-Version: 1.0 Main-Class: package.MainClassName (blank line) ``` and is in the `META-INF` folder. There is a folder with my package name, which contains all the .class files, including the class that contains the main method. A few image and text files that I use also appear in the jar file. The actual program isn't anything too complicated -- it's a simple "snake" game using Swing (plus the code all works when run from inside Eclipse). Any ideas what is causing this error and how I can fix it? Let me know if there's any other information I should provide.