Certain older versions, a corrupt button Cache could make an otherwise "good" ITM later show up as unsupported.
Go into CADmep and run the REFRESHALLBTNS command.
By default, when you open CADmep, you'll see a "Locating Invalid Buttons" progress bar in the lower left of AutoCAD. When you press "ESC" to cancel this, that's when the button cache gets corrupted.
You don't want to hit ESC during this process.
You can also go into the Edit Config program for CADmep and select the "Skip Validate Buttons at Start-Up" to keep this scan from happening in the future. Note however that this setting is "per user" and "per version" on a computer.