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Incompatible Web Part markup detected. Use *. dwp web part XML instead of *. webpart web part XML.

If you have created your own web part and getting this error message then it is because the Web Part inherit from the wrong class. You must inherit from the following class:

System.Web.UI.WebControls.WebParts.WebPart

and NOT:

Microsoft.SharePoint.WebPartPages.WebPart

If you get the error message above Mentioned, then you inherit from the wrong class in your custom webpart. It is supposed to inherit from:

System.Web.UI.WebControls.WebParts.WebPart and NOT: webpart
Here is a little example how to create your custom:: Microsoft.SharePoint.WebPartPages.WebPar

Here's a small example of how to create your own Web
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