When you are specifying required JAR files or modules, you first specify the enterprise application (EAR) that your project is a part of. Typically, the project is referenced by one EAR project in the workspace. However, it is possible that you have multiple enterprise applications that contain a reference to the same module or utility JAR project. If so, then ensure that you give the JAR or module the same Uniform Resource Identifier (URI) in each application, so that the class path is valid for all applications.
It is also possible that your module is a standalone project and is not currently referenced by any enterprise application. In this case, since there is no enterprise application scope defined, you cannot use the Manifest editor to update the dependencies. To add the module to an enterprise application, see Adding modules to an enterprise application.