Valid for Sitecore 6.x
  Error message in the Content Editor

Reference Number: 328877.

In some cases, particularly during high server load, the Content Editor may receive the error message "Multiple controls with the same ID were found".
Workaround:
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 value of __Skin field or ContentEditor.DefaultSkin setting). All items will be rendered with the default skin.