A Web Part or Web Form Control on this Web Part Page cannot be displayed or imported because it is not registered on this site as a safe control

Cause:

The error (A Web Part or Web Form Control on this Web Part Page cannot be displayed or imported because it is not registered on this site as a safe control) indicates a problem with the installation (deployment) of the product, ie: a necessary file was not deployed successfully to all Web Front Ends, or our Code Access Security policy was not applied successfully to the Web Application(s).

Resolution:

To resolve, please reinstall the product using one of the following methods:

• In Central Administration > Operations > Solution Management: Retract and the re-Deploy the solution (.wsp) to your Web Applications

OR

• Using the product installation scripts, uninstall and reinstall the product
• NOTE: resetting IIS and the WSS Timer service on all farm servers running the SharePoint Web Application service can help, before installing (deploying) a product into SharePoint