Cannot generate access tokens in WSO2 API Manager - wso2

Question

I just set up WSO2 API Manager on a cloud server. Most of it currently works, but unfortunately I cannot generate access tokens. This is the error I observe:
TID: [-1234] [] [2016-01-14 15:12:15,866] ERROR {org.apache.catalina.core.StandardWrapperValve} - Servlet.service() for servlet [OAuth2Endpoints] in context with path [/oauth2] threw exception {org.apache.catalina.core.StandardWrapperValve}
java.lang.RuntimeException: org.apache.cxf.interceptor.Fault
at org.apache.cxf.interceptor.AbstractFaultChainInitiatorObserver.onMessage(AbstractFaultChainInitiatorObserver.java:116)
at org.apache.cxf.phase.PhaseInterceptorChain.doIntercept(PhaseInterceptorChain.java:336)
at org.apache.cxf.transport.ChainInitiationObserver.onMessage(ChainInitiationObserver.java:121)
at org.apache.cxf.transport.http.AbstractHTTPDestination.invoke(AbstractHTTPDestination.java:249)
at org.apache.cxf.transport.servlet.ServletController.invokeDestination(ServletController.java:248)
at org.apache.cxf.transport.servlet.ServletController.invoke(ServletController.java:222)
at org.apache.cxf.transport.servlet.ServletController.invoke(ServletController.java:153)
at org.apache.cxf.transport.servlet.CXFNonSpringServlet.invoke(CXFNonSpringServlet.java:171)
at org.apache.cxf.transport.servlet.AbstractHTTPServlet.handleRequest(AbstractHTTPServlet.java:289)
at org.apache.cxf.transport.servlet.AbstractHTTPServlet.doPost(AbstractHTTPServlet.java:209)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:646)
at org.apache.cxf.transport.servlet.AbstractHTTPServlet.service(AbstractHTTPServlet.java:265)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:303)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
at org.wso2.carbon.ui.filters.CSRFPreventionFilter.doFilter(CSRFPreventionFilter.java:88)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
at org.wso2.carbon.ui.filters.CRLFPreventionFilter.doFilter(CRLFPreventionFilter.java:59)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:220)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:122)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:504)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:170)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:103)
at org.wso2.carbon.tomcat.ext.valves.CompositeValve.continueInvocation(CompositeValve.java:99)
at org.wso2.carbon.tomcat.ext.valves.CarbonTomcatValve$1.invoke(CarbonTomcatValve.java:47)
at org.wso2.carbon.webapp.mgt.TenantLazyLoaderValve.invoke(TenantLazyLoaderValve.java:57)
at org.wso2.carbon.tomcat.ext.valves.TomcatValveContainer.invokeValves(TomcatValveContainer.java:47)
at org.wso2.carbon.tomcat.ext.valves.CompositeValve.invoke(CompositeValve.java:62)
at org.wso2.carbon.tomcat.ext.valves.CarbonStuckThreadDetectionValve.invoke(CarbonStuckThreadDetectionValve.java:159)
at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:950)
at org.wso2.carbon.tomcat.ext.valves.CarbonContextCreatorValve.invoke(CarbonContextCreatorValve.java:57)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:116)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:421)
at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1074)
at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:611)
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1739)
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.run(NioEndpoint.java:1698)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
at java.lang.Thread.run(Thread.java:745)
Caused by: org.apache.cxf.interceptor.Fault
at org.apache.cxf.service.invoker.AbstractInvoker.createFault(AbstractInvoker.java:170)
at org.apache.cxf.service.invoker.AbstractInvoker.invoke(AbstractInvoker.java:136)
at org.apache.cxf.jaxrs.JAXRSInvoker.invoke(JAXRSInvoker.java:204)
at org.apache.cxf.jaxrs.JAXRSInvoker.invoke(JAXRSInvoker.java:101)
at org.apache.cxf.interceptor.ServiceInvokerInterceptor$1.run(ServiceInvokerInterceptor.java:58)
at org.apache.cxf.interceptor.ServiceInvokerInterceptor.handleMessage(ServiceInvokerInterceptor.java:94)
at org.apache.cxf.phase.PhaseInterceptorChain.doIntercept(PhaseInterceptorChain.java:272)
... 44 more
Caused by: java.lang.NullPointerException
at org.wso2.carbon.identity.oauth2.OAuth2Service.issueAccessToken(OAuth2Service.java:214)
at org.wso2.carbon.identity.oauth.endpoint.token.OAuth2TokenEndpoint.getAccessToken(OAuth2TokenEndpoint.java:245)
at org.wso2.carbon.identity.oauth.endpoint.token.OAuth2TokenEndpoint.issueAccessToken(OAuth2TokenEndpoint.java:111)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:497)
at org.apache.cxf.service.invoker.AbstractInvoker.performInvocation(AbstractInvoker.java:188)
at org.apache.cxf.service.invoker.AbstractInvoker.invoke(AbstractInvoker.java:104)
... 49 more
TID: [-1234] [] [2016-01-14 15:12:15,938] ERROR {JAGGERY.site.blocks.subscription.subscription-add.ajax.subscription-add:jag} - java.lang.RuntimeException: Error occurred while calling token endpoint: HTTP error code : 500 {JAGGERY.site.blocks.subscription.subscription-add.ajax.subscription-add:jag}
Does anyone have a clue what is going on? I didn't observe any startup warnings or errors.
Update: Since I was asked for a bit more configuration information, this is what I changed from the default config files.
I set the HostName in carbon.xml to my address
I changed the ServerURL and the GatewayEndpoint (APIGateway -> Environments -> Environment(type="hybrid")) to contain my address rather than the local IP. This was changed in the api-manager.xml.
The firewall allows connections to port 8280, 8243, 10397, 9763 & 9443.