The latest build of GTC might be an unsigned FlashApp. You have three solutions, sorted from easiest to hardest:
* execute Flashappy on your 89T, which will permanently disable the FlashApplication signature check;
* resign the FlashApp using RabbitSign and the 0103 (or 0109) key;
* use the binary diffs distributed alongside tiosmod+amspatch (which contains 14 changes besides Flashappy) to patch AMS 3.10 for 89T, backup your calculator, and transfer the patched AMS to your calculator.