Errorcode "9" in offline oData application

Hello

I am working with a offline application and the oData kapsel plugin, when I am saving as draft I receive this error from the backend debugging in a Windows 8.1 app.

An error occurred or user cancelled action: {"message":{"errorCode":"9","errorMessage":"call to unexpected method.\r\n\r\n This is not a string value. Use ValueType property to get the type.","errorDomain":"OfflinePluginErrorDomain"}}

Any clue about this topic? Running under iOS without problem.

Thank you in advance.

Óscar.