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When I open any page in SharePoint Designer I receive an error that says: Error Creating Control - WebPartAdderUpdatePanel
Unknown server tag 'WebPartPages:WebPartAdder'.

I still seem to be able to use SharePoint Designer without any problems. Any ideas what might cause this, and how can I fix it?

Thank you for your help.

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Position has already been activated, reactivation did not help – Silva de Vuple Jun 17 '14 at 10:49
up vote 2 down vote accepted

I had the same issue when editing the master pages for the 'Companyweb' site on SBS 2011.

It seems to be permissions related and I was able to get rid of the error by logging into sharepoint with the site owner account (as opposed to a 'normal' site editor) and did the following:

  1. Go to 'Site Actions' at the top right of the page then click on 'Site Settings'
  2. Under 'Site Collection Administration' select 'SharePoint Designer Settings'
  3. Tick 'Enable Managing of the Web Site URL Structure'

After doing this the error went away.

I should point out that I'm new to SharePoint and 'just fiddling' rather than dealing with a production site, so I can't comment on whether or not it's actually a good idea to do this or not!

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Unfortunately, this did not work ! Anyone else?? – user38988 Jan 23 '15 at 23:56

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