Safe Control enteries in your web.config for the particular web application.(sharepoint 2010)

Web Part Error: A Web Part or Web Form Control on this Page cannot be displayed or imported. The type SunInt.Hrda.SharePoint.MaintainBudget.MaintainBudget, SunInt.Hrda.SharePoint, Version=1.0.0.0, Culture=neutral, PublicKeyToken=b21a70e7493d978f could not be found or it is not registered as safe.

1. Select your custom webpart
2. Use right click > Properties
3. In properties windows under SharePoint find Safe Control Entries
4. Click ... button
5. Verify your settings (namespace)