I created a simple visual web part(farm solution only) with Hello World text in it and added in a SitePage through browser which is working fine.

Now when I open that page in SP Designer 2013 and just saves it without modifying anything on page, and tries to preview it in browser, it gives error.

Error Web Part Error: Unknown server tag 'wpns0:TestVisualWebPartACE'. Correlation ID: 63c08e9d-2313-9032-f671-d6883bc7b7c2

It gave same error when I re-inserted that web part in that page through SP Designer.

Can anyone please suggest what might be the issue?

1 Answer 1


Unknown server tag means that when parsing the site page the tag wpns0:TestVisualWebPartACE

So via SharePoint designer Check the top of your site page that its register tag and make sure that the tag prefix is the same that used in your visual web part.

For examble :

<%@ Register Tagprefix="WebPartPages" Namespace="Microsoft.SharePoint.WebPartPages" Assembly="Microsoft.SharePoint, Version=, Culture=neutral, PublicKeyToken=71eqw23111e9429c" %>
  • I checked and all the tags are properly registered on the top of the page.
    – Yayati
    Commented Jul 12, 2016 at 6:28

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