Known Issue: "Toolbar 'Custom' does not exist!" and Work Around
If you create an HTMLEditor preset using the Preset Manager and remove items from the toolbar, a javascript error will occur when viewing pages that use the preset:
"Toolbar 'Custom' does not exist!"
To work around the problem, create the preset while applying the HTMLEditor instance to the page instead of through the preset manager.
Go to Insert -> WebAssist -> HTMLEditor
Click the customize button next to preset and modify the toolbar buttons. When you click OK you will be prompted to save a preset.
You can then apply the saved preset to other pages without getting the javascript Error.