Editing a Simple HTML message in the Email Experience Manager (EXM) can result in an error. The toolbars are not shown after clicking Save. The following message might be displayed in the browser console:
VM2182 13212132646491421379.js:15130 Uncaught TypeError: Cannot read property 'document' of null at top.initModalDialog (VM2182 13212132646491421379.js:15130)This issue affects EXM 9.0 Update-1 - 9.3 Initial Release.
To resolve the issue, download and install the patch available on this page:
https://github.com/SitecoreSupport/Sitecore.Support.250864/releases.
To get a solution for other releases, contact Sitecore Support.