I was using Weaver 11 theme for my web site, and would like to use a newer theme such as WeaverXtreme. I am unable to delete one particular widget, and it doesn’t matter what theme I try to use, I am unable to access the widget to edit it, and am stuck with the widget appearing on my web site.
When I open Appearance-Widgets I have two errors listed at the top, both of which state “The “addthis_tool_by_class_name_widget” block was affected by errors and may not function properly.”
The problem is in the Primary (top) sidebar – if I try to expand this to see what’s in there I just look at a constantly rotating “loading” circle going round and round.
You have not provided a link, but from the error description you provided it sounds like an error with some widget you’ve added with a plugin. But from the information you provided, the problem almost certainly has nothing to do with whatever theme you are using.
One way to track this down is to temporarily disable any plugins you may be using one at a time (or a small group of plugins to at least find which plugins to target) until the error message goes away.