Google is sometimes a great help with things like this. Other times, you can't find an article you can understand.
When posting bugs, make sure to mention what Java version and build number your using. Find it in the Java control panel under Control Panel in Windows, "About..." button.
From the few results I spotted, there's a good chance you probably need to reinstall Java. Either Java SE v6 or v7 should work with Haven & Hearth, but if you're having issues with 7, you might need to install Java 6. (v7 is only a few months old and, as with most new software, has some bugs that need to be worked out or compatibility problems.)
Opinions expressed in this statement are the authors alone and in no way reflect on the game development values of the actual developers.