Do you have more than one GameHelper.java classes floating around? Have you compiled the GameHelper.java file before using it?
Also, when posting code here, please use code tags so that your code will retain its formatting and thus will be readable -- after all, your goal is to get as many people to read your post and understand your code as possible, right?
To do this, highlight your pasted code (please be sure that it is already formatted when you paste it into the forum; the code tags don't magically format unformatted code) and then press the code button, and your code will have tags.
Another way to do this is to manually place the tags into your code by placing the tag [code] above your pasted code and the tag [/code] below your pasted code like so:
Welcome to the Ranch! Please be sure to use code tags when posting code to the forums. Unformatted or unindented code is extremely hard to read and many people that might be able to help you will just move along to posts that are easier to read. Please click this link ⇒ UseCodeTags ⇐ for more information.
Properly indented and formatted code greatly increases the probability that your question will get quicker, better answers.