vt7.4 - CKEditor Spell Check locks browser

Open a Contact, and click Send Email. In the CKEditor text area click the spell check button - a popup appears, but then cannot be closed or exited. Have to close browser tab and re-open.

Browser console records the following errors:

Failed to load resource: the server responded with a status of 403 () Uncaught ReferenceError: DefaultParams is not defined at Object. (/vtigercrm/libraries/jquery/ckeditor/plugins/wsc/dialogs/wsc.js?t=DBAA:31:281) at o (ckeditor.js:214:177) at Array.q (ckeditor.js:214:336) at s (ckeditor.js:214:420) at HTMLScriptElement.f.$.onerror (ckeditor.js:215:361) Uncaught TypeError: Cannot read properties of null (reading 'setDisable') at Object. (/vtigercrm/libraries/jquery/ckeditor/plugins/wsc/dialogs/wsc.js?t=DBAA:67:432) at CKEDITOR.dialog.i (ckeditor.js:10:222) at CKEDITOR.dialog.fire (ckeditor.js:12:32) at button.onClick (ckeditor.js:538:363) at button. (ckeditor.js:480:194) at button.i (ckeditor.js:10:222) at button.fire (ckeditor.js:12:32) at button.click (ckeditor.js:479:261) at CKEDITOR.dom.element. (ckeditor.js:471:58) at CKEDITOR.dom.element.i (ckeditor.js:10:222)