The "java.lang.ClassFormatError: Invalid method Code length" error, is an error that you can get generating the layout of your Web Project, it means that you used a template in the Web Project that is too large to be compiled.
Read this article to discover more about how to handle and prevent this ...
The UnsupportedClassVersionError can occurr in a Web Project that uses custom components, such as custom validation rules, servlets or listeners.
All these components are developed using a different project (e.g. a Java project) in which you have to compile the Java classes and create a jar file...