This happens on IE 11 only so far (OS=windows 8.1). When you make the textbox visible to false, it causes javascript error. Please fix this bug. (sample attached).
Comments: I have installed AjaxControlToolkit 15.1.2.0 however this problem still occurs so it does not look like it is resolved. When running HTMLEditorExtender in IE11 it crashes with 0x800a139e - JavaScript runtime error: IndexSizeError on line: sel.collapse(this._editableDiv.firstChild, char); It only works if you use <meta http-equiv="X-UA-Compatible" content="IE=10" />
Comments: I have installed AjaxControlToolkit 15.1.2.0 however this problem still occurs so it does not look like it is resolved. When running HTMLEditorExtender in IE11 it crashes with 0x800a139e - JavaScript runtime error: IndexSizeError on line: sel.collapse(this._editableDiv.firstChild, char); It only works if you use <meta http-equiv="X-UA-Compatible" content="IE=10" />