You may have this error when upgrading to a major version of Appeon or installing an EBF (see attached).

Before contacting Appeon support please be sure of doing a FULL deployment of your application with the new version.

If you are using Websphere you need to undeploy the application and then redeploy it (full deployment) 

If after doing a FULL deployment you still have the error, the issue is probably caused by the different Web root between the web server and the application server.

In the case of IIS the is solution to check if the application exist under the web root of the IIS. If it is the case you need to change the web root of the web server to make it be the same as the IIS (please see attached)