A Web Part or Web Form Control on this Page cannot be displayed or imported. The type could not be found or it is not registered as safe.

Solution:

Try to Clean your entire application solution package
recycle IIS
build the solution again
and then try to deploy it on sharepoint server

to view the deployed webpart

after successfull deployment
open sharepoint website where webpart is deployed
go to SiteActions -> Site Settings
Click on Webparts under Galleries
click on NewDocument -> select the webparts you have deployed
then click on Populate Gallery
now you can see the webpart you have deployed it the list


Adding webpart into page

go to the page where you want to add webpart
click on edit page mode
click on add webpart
then select the webpart from the group and click on add button