This issue is typically caused by wrong configuration/deployment of charts.
First, please check to make sure the proper VitaraCharts plugin is deployed; In the case of mobile, the plugin to download is called VitaraChartsMobile.zip
Follow all the installation steps listed in the install guide for mobile.
Note that after deploying, the plugins folder will have several Vitara related folders (one for each type of chart)
In case a cluster of mobile servers are being used, it is critical to ensure Vitaracharts is deployed to all nodes in the cluster.
Also please verify that the version of Charts deployed in Mobile and Web both are same.
If you are using VitaraCharts for Documents please make sure that Display widget option in (iPhone, iPad,Android..etc) is enabled for the widget.