New Event>Message tab is grayed out

When creating a New Event, either from the Calendar or via Activities>Scheduling>Events>New, the Message tab is grayed out and Text Editor is inaccessible.

To resolve this, perform the following:

1. Use a Standard Event Form.  If the ability to edit is present on a standard form, check the Custom Event Form's settings.

• Navigate to Customization > Forms > Entry Forms
• Click Edit on the Custom Event Form in question
• Click the Fields tab > Message subtab
• Ensure that the Display Type for Message is not set as Disabled

2. If still grayed out on a Standard Event Form, try a different browser.
3. Clear browser cache if able to edit the Message tab when on a different browser.

Note: Steps above can be performed when the issue happens on an existing event.  However, Permission and Event restrictions (e.g. Calendar preferences) have to be considered as well.