I can't think why it's behaving like that, if it's a genuine original Garmin SD card.
I certainly would not re-purchase the maps in this case.
You've already purchased them, and are entitled to use them.
If it were me, at this stage, I would just totally unlock the image using SPESHUL TOOLS and be done with it.
But that is the language of the Dark Side, and I shall not utter it here.
PM if you want to try this.