You are not normally supposed to see any green info bar to begin with, because that line means that GSX is trying to tell you something went wrong, like trying to use it without parking brakes, or in a parking too small, or any other warning.
However, fact you cannot read the text inside, is entirely outside our control because what GSX does, is to simply use the standard Simconnect command to display this text, but whether you can read it or not, it's entirely depending on FSX.
- Try to put FSX in a Window (if you normally use Full screen), pressing ALT+Enter and see if the message is visible.
- Check you haven't touched the settings in the FSX.CFG that controls the info bar colors: maybe both the text and the background has been set to the same color, so you cannot see the text. If you don't know how to change them, delete your FSX.CFG, located at %APPDATA%\Microsoft\FSX, so FSX will rebuild a new one with default settings.
- Be sure you don't have another addon that is trying to write to the info bar at the same time. Concurrent messages should be queued, but there are some addons that don't use Simconnect and write directly to FSX memory, which might cause issues, although nobody ever reported this, it's still a possibility.