Dear lydia0500,
I am using dnn5.1.4, I installed it in my local computer and have a full test and it work well, I cannot reproduce this issue.
The configuration file can be found at:
DNN050104\Providers\HtmlEditorProviders\CEHtmlEditorProvider\CuteSoft_Client\CuteEditor\Configuration\Security\admin.config,
Please post its content here.
Please also post this error's screen shot here.
Regards,
Eric