Eclipse - JAR创建失败的“类路径文件没有找到或无法访问…”

I have a project in Eclipse which has a red cross on it and will not export to a runnable JAR. I can't remember if I have looked at it since I reinstalled Windows on my laptop, but I know that I haven't changed any code. There are no errors in any of the classes, however the error I get points to the following class which deals with the menu items on Mac OSx:I have a project in Eclipse which has a red cro