Error changing namespace in Webpart

I had a Webpart that due naming conventions I have to change the namespace of the main class.

But when I change the old namespace to the new namespace, and I deploy the webpart, I get this message.

Why this occurs?

EDIT:

Response (the page don't let me answer my own question)

It was the .webpart file, that mantai开发者_如何学JAVAns the old mamespace

<metaData>
    <type name="OLDNAMESPACE.NameWebpart, $SharePoint.Project.AssemblyFullName$" />
    <importErrorMessage>$Resources:core,ImportErrorMessage;</importErrorMessage>
</metaData>

http://socialsp.com/2010/08/24/changing-namespace-in-visual-studio-2010-might-break-a-sharepoint-2010-webpart-project/

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Check your SafeControl settings in your Web.Config and ensure you're including the assembly and relevant namespaces in the configuration.

Also ensure that, if using a strongly typed assembly, the latest build has been dropped into the GAC.