We no longer support RadEditor for MCMS. The RadEditorPlaceholderControl's development is discontinued since the end of 2007, and the control was supported until the end of 2008. This information was sent to all RadEditorPlaceholderControl users in the middle of 2007 and announced on our site as well.
I also searched our records for the reported error, but I was unable to find any information that applies to it.
My suggestion is to test the latest available hotfix version 7.3.4 and see whether the problem still persists. For your convenience I have attached the trial build.
If the hotfix solves the issue, please open a support ticket and request the registered build.
the Telerik team
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