What no one has outright said, is that it appears this error message means "The antenna SWR is excessive, it ain't being matched (tuned) correctly."
So the #1 thing to troubleshoot is the antenna connection & antenna, followed by checking the "tuner" to make sure that is operating. You'd need a second person to literally listen carefully at the tuner, so see if it shows any signs of life (clicking, etc.) on those bands.
Odds are that it is properly tuning the other bands, that it is working, and the problem comes back to the antenna/connection. You mention the GTO15 is new. If it was installed too close to some part of the rigging
, or was grounding to it, that could also be the kind of subtle installation
problem that could take it out of the tuner's range.