project_key: JBEPP

When trying to add a gadget type portlet to a page, the following error occurs:

Unable to retrieve spec for http://localhost:8080/rest/jcr/repository/portal-system/production/app:gadgets/app:Calculator/app:data/app:resources
/Calculator.xml. HTTP error 500

12:58:11,986 ERROR [[RestServer]] Servlet.service() for servlet RestServer threw exception
javax.ws.rs.WebApplicationException
	at org.exoplatform.services.rest.impl.ContainerResponse.writeResponse(ContainerResponse.java:195)
	at org.exoplatform.services.rest.impl.RequestHandlerImpl.handleRequest(RequestHandlerImpl.java:249)
	at org.exoplatform.services.rest.servlet.RestServlet.onService(RestServlet.java:85)
	at org.exoplatform.container.web.AbstractHttpServlet.service(AbstractHttpServlet.java:132)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
	at org.exoplatform.services.rest.servlet.RestEncodingFilter.doFilter(RestEncodingFilter.java:58)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
	at org.exoplatform.frameworks.jcr.web.ThreadLocalSessionProviderInitializedFilter.doFilter(ThreadLocalSessionProviderInitializedFilter.java:116)