Issue
You edit a Mtext and the icons become disabled on the ribbon.

Solution
The ribbon becomes grayed out when the acad.cuix is loaded at the same time than the aca.cuix.
To enable the icons, unload the acad.cuix. Follow these steps:

Type MENULOAD at the command line.
1. In the Load/Unload Customizations dialog box, select ACAD in the list.
2. Click Unload.
3. Click Close to close the Load/Unload Customizations dialog box.
4. If you want to use ribbons, menus from the acad.cuix file, use the Transfer tab from the Customize User Interface (CUI).