Hi,
Based on my understanding, I think you want to access class Codefile5 from class Codefile1, right?
By default, the classes that are in the App_Code folder are available in whole website. So we need to make sure that this class is Public and the Namespace is correct if it has.
Besides, did we set the compile order for these sub-directories of App_Code? If we set codeSubDirectories collection (http://msdn.microsoft.com/en-us/library/54dwfbb7.aspx) in web.config, the class that is in the sub-directory will be built firstly, and then the class that is in the root of App_Code directory is built last. If so, we cannot access class Codefile5 from class Codefile1.
I look forward to hearing from you.