I have an application using gwt and hosted on gae. There is a form using xfbml and having a redirect url once data is filled and form is submit. the problem is it throws exception if this happens via xfbml form submit. if i invoke the url directly it works great. 

The xfbml code is:

```
<fb:registration redirect-uri="http://www.sakshum.org/FbBloodDonorRegister" fields='[{"name":"name"},{"name":"first_name"},{"name":"last_name"}, {"name":"cellPhone", "description":"Cell Number", "type":"text"}, {"name":"homePhone", "description":"Home Number", "type":"text"}]'  onvalidate="validated" width="530">
</fb:registration>

```

The exception is below

```
javax.servlet.ServletContext log: Exception while dispatching incoming RPC call
javax.servlet.ServletException: Content-Type was 'application/x-www-form-urlencoded'. Expected 'text/x-gwt-rpc'.
    at com.google.gwt.user.server.rpc.RPCServletUtils.checkContentTypeIgnoreCase(RPCServletUtils.java:427)
    at com.google.gwt.user.server.rpc.RPCServletUtils.readContent(RPCServletUtils.java:160)
    at com.google.gwt.user.server.rpc.RPCServletUtils.readContentAsGwtRpc(RPCServletUtils.java:205)
    at com.google.gwt.user.server.rpc.AbstractRemoteServiceServlet.readContent(AbstractRemoteServiceServlet.java:182)
    at com.google.gwt.user.server.rpc.RemoteServiceServlet.processPost(RemoteServiceServlet.java:239)
    at com.google.gwt.user.server.rpc.AbstractRemoteServiceServlet.doPost(AbstractRemoteServiceServlet.java:62)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:637)
    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$CachedChain.doFilter(ServletHandler.java:1166)
    at com.google.apphosting.utils.servlet.ParseBlobUploadFilter.doFilter(ParseBlobUploadFilter.java:102)
    at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
    at com.google.apphosting.runtime.jetty.SaveSessionFilter.doFilter(SaveSessionFilter.java:35)
    at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
    at com.google.apphosting.utils.servlet.TransactionCleanupFilter.doFilter(TransactionCleanupFilter.java:43)
    at org.mortbay.jetty.servlet.ServletHandler$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.apphosting.runtime.jetty.AppVersionHandlerMap.handle(AppVersionHandlerMap.java:249)
    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$RequestHandler.headerComplete(HttpConnection.java:923)
    at com.google.apphosting.runtime.jetty.RpcRequestParser.parseAvailable(RpcRequestParser.java:76)
    at org.mortbay.jetty.HttpConnection.handle(HttpConnection.java:404)
    at com.google.apphosting.runtime.jetty.JettyServletEngineAdapter.serviceRequest(JettyServletEngineAdapter.java:135)
    at com.google.apphosting.runtime.JavaRuntime$RequestRunnable.run(JavaRuntime.java:447)
    at com.google.tracing.TraceContext$TraceContextRunnable.runInContext(TraceContext.java:452)
    at com.google.tracing.TraceContext$TraceContextRunnable$1.run(TraceContext.java:458)
    at com.google.tracing.TraceContext.runInContext(TraceContext.java:698)
    at com.google.tracing.TraceContext$AbstractTraceContextCallback.runInInheritedContextNoUnref(TraceContext.java:336)
    at com.google.tracing.TraceContext$AbstractTraceContextCallback.runInInheritedContext(TraceContext.java:328)
    at com.google.tracing.TraceContext$TraceContextRunnable.run(TraceContext.java:456)
    at com.google.apphosting.runtime.ThreadGroupPool$PoolEntry.run(ThreadGroupPool.java:251)
    at java.lang.Thread.run(Thread.java:679)

```