This error appears when attempting to start an an application in IBM WebSphere.
In the left panel of WebSphere, expand Troubleshooting and select Logs and trace. Then select the server that contains the application that failed to start.
Select View HPEL logs and trace.
In this example, the log file identifies the cause of the problem. When the application was created, the context of / (root) was used, but this context has already been used by the DefaultApplication. In this scenario, update the application to use a context other than / (root).