If the version of RadEditor used is outdated and older than the release of the IE11 browser, incompatibility issues are expected to occur. If so, it is suggested to upgrade.
If you are using a recent version, please, provide some more details or code samples of the configuration leading to the thrown error.
Do you want to have your say when we set our development plans?
Do you want to know when a feature you care about is added or when a bug fixed?
Telerik Feedback Portal
and vote to affect the priority of the items