Google App Engine - Failed to retrieve API configs with status: 404 - google-app-engine

Question

I'm using Google App Engine to develop a plugin for Atlassian JIRA. They have recently changed around how to use development instances of Cloud JIRA. It now uses an external, Atlassian hosted, version of JIRA Cloud (instead of a local copy).
To develop locally you need to run ngrok (atlassian instructions) to communicate between your local server (for me Google App Engine running in Eclipse) and the external JIRA instance.
My problem is that this gives a 500 error reporting a 404 when it does the AJAX call to the Google App Engine end point. The Servlet calls work fine. The Javascript error is:
jquery.min.js:4 GET https://7d45c4d7.au.ngrok.io/_ah/api/myplugin/v1/addEdit?projectId=10001&id=-1 500 (Failed to retrieve API configs with status: 404)
The returned error if I try to put the URL into my browser is:
HTTP ERROR 500
Problem accessing /_ah/api/myplugin/v1/addEdit. Reason:
Failed to retrieve API configs with status: 404
Caused by:
java.io.IOException: Failed to retrieve API configs with status: 404
at com.google.api.server.spi.tools.devserver.ApiServlet.getApiConfigSources(ApiServlet.java:107)
at com.google.api.server.spi.tools.devserver.ApiServlet.initConfigsIfNecessary(ApiServlet.java:72)
at com.google.api.server.spi.tools.devserver.RestApiServlet.service(RestApiServlet.java:117)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
at org.mortbay.jetty.servlet.ServletHolder.handle(ServletHolder.java:511)
at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1166)
at com.google.appengine.api.socket.dev.DevSocketFilter.doFilter(DevSocketFilter.java:74)
at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
at com.google.appengine.tools.development.ResponseRewriterFilter.doFilter(ResponseRewriterFilter.java:128)
at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
at com.google.appengine.tools.development.HeaderVerificationFilter.doFilter(HeaderVerificationFilter.java:34)
at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
at com.google.appengine.api.blobstore.dev.ServeBlobFilter.doFilter(ServeBlobFilter.java:63)
at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
at com.google.apphosting.utils.servlet.TransactionCleanupFilter.doFilter(TransactionCleanupFilter.java:50)
at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
at com.google.appengine.tools.development.StaticFileFilter.doFilter(StaticFileFilter.java:125)
at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
at com.google.appengine.tools.development.DevAppServerModulesFilter.doDirectRequest(DevAppServerModulesFilter.java:366)
at com.google.appengine.tools.development.DevAppServerModulesFilter.doDirectModuleRequest(DevAppServerModulesFilter.java:349)
at com.google.appengine.tools.development.DevAppServerModulesFilter.doFilter(DevAppServerModulesFilter.java:116)
at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
at org.mortbay.jetty.servlet.ServletHandler.handle(ServletHandler.java:388)
at org.mortbay.jetty.security.SecurityHandler.handle(SecurityHandler.java:216)
at org.mortbay.jetty.servlet.SessionHandler.handle(SessionHandler.java:182)
at org.mortbay.jetty.handler.ContextHandler.handle(ContextHandler.java:765)
at org.mortbay.jetty.webapp.WebAppContext.handle(WebAppContext.java:418)
at com.google.appengine.tools.development.DevAppEngineWebAppContext.handle(DevAppEngineWebAppContext.java:98)
at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152)
at com.google.appengine.tools.development.JettyContainerService$ApiProxyHandler.handle(JettyContainerService.java:513)
at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152)
at org.mortbay.jetty.Server.handle(Server.java:326)
at org.mortbay.jetty.HttpConnection.handleRequest(HttpConnection.java:542)
at org.mortbay.jetty.HttpConnection$RequestHandler.headerComplete(HttpConnection.java:923)
at org.mortbay.jetty.HttpParser.parseNext(HttpParser.java:547)
at org.mortbay.jetty.HttpParser.parseAvailable(HttpParser.java:212)
at org.mortbay.jetty.HttpConnection.handle(HttpConnection.java:404)
at org.mortbay.io.nio.SelectChannelEndPoint.run(SelectChannelEndPoint.java:409)
at org.mortbay.thread.QueuedThreadPool$PoolThread.run(QueuedThreadPool.java:582)
I have searched around and the only thing I can find is to add --address=0.0.0.0 to the program arguments (next to --port=8888) but this still doesn't work (actually makes no difference).
I found another article that said they got this type of error when not using #Named on the on the parameters being passed in but I have these for the called code.
Any ideas?
Thanks
Paul