In some cases, particularly during high server load, the Content Editor may receive the following error message:
Multiple controls with the same ID 'FIELD20611532_container' were found. FindControl requires that controls have unique IDs.
Comment out the following processor in your web.config file:
<processor type="Sitecore.Shell.Applications.ContentEditor.Pipelines.RenderContentEditor.RenderSkinedContentEditor, Sitecore.Client"/>
This will instruct the Content Editor to ignore Skin settings for the current item (taken from the value of __Skin field or ContentEditor.DefaultSkin setting). All items will be rendered with the default skin.