Few things are more frustrating then spending 30+ minutes customizing the mapdata.js only to find that the map won't load. One way to avoid this problem is to save the mapdata.js frequently and check your progress as you go. If the map fails to load, you can just undo your most recent changes and quickly identify your error. However, this can be slow and isn't always practical.
Fortunately, errors are usually easy to identify because the problem is almost always the same:
If the page won't load, 90% of time, there is a missing (or extra) comma in the mapdata.js file.
To determine where the problem is located, do the following:
If the map works in all browsers except Internet Explorer 7
That means that you left an extra comma after the last property in an object in the mapdata.js file. This is ok in all other browsers, but will throw an error in IE7. The following image shows you an example of omitting commas: