Make sure that SimpleProxyServlet is working by following this steps:
1) Open your web.xml and find application name.
2) Try to access your OData service via tomcat's proxy (please make sure tomcat is up and running) - replace "mySuperApp" to applciation name you find in step 1.
http://localhost:8080/mySuperApp/proxy/sap/opu/odata/sap/SRA006_SRV/$metadata
Let us know about results.
Regards,
Vladimir