After recoding my CMSAbstractLayoutWebPart tens of times because I thought it was my fault that the widgets in it where not reordering, I noticed in the console that whilst on the cms on the page and design tabs I get the following error Sys.ArgumentException: Value must be null for Components that are not Controls or Behaviors. Parameter name: element
SCRIPT5022: Sys.ArgumentException: Value must be null for Components that are not Controls or Behaviors.Parameter name: elementScriptResource.axd (4624,23)
Chrome: ScriptResource.axd?d=Ry27Zmqk4PbGnGHSG9wx2yVpE_1jrrzvy6NRsZPVzvU8CSNTTUn7l_AgmYnyJJDXwf5B2ASdSaco3A…:847 Uncaught Sys.ArgumentException: Sys.ArgumentException: Value must be null for Components that are not Controls or Behaviors.Parameter name: element
Could you please check, if your master page uses ajaxToolkit:ToolkitScriptManager, and if so if it has ScriptMode=”Release” set?
Did you recently upgrade to 8.2 from and earlier version?
I am seeing the same issues on my project that is a fresh install of 8.2 with hotfix 46. I see the console errors mentioned above when I am working on the design tab trying to add or remove webparts from webpartzones.
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