You got this error because this assembly isn't not registered as safe in your web.config. By default Virto Components add it automatically. You can try just reinstall the product using setup.exe. If you issue persists you have to add a safe entry manually to your web.config. To do it please follow steps.
- Log in to your WFE server
- Open web.config for specific web application. The web.config is located at C:\inetpub\wwwroot\wss\VirtualDirectories\[web applicaiton post] folder.
- Add following entry to <SafeControls> section <SafeControl Assembly="[full assembly name]" Namespace="[namespace]" TypeName="*" Safe="True" />