Hello.
Just a few hardware related guesses.
All SD cards use 3.3V. KIT-043 is 5V. You may have damaged the microSD card. You need to add a 3.3V regulator or, you can power KIT-043 from a 3.3V power supply but you'll need to remove diode D1 from KIT-043. If you don't remove this diode and you plug KIT-043 into USB, the USB 5V will over-ride the external 3.3V power supply.
The SD electrical interface operates at a reasonable high speed. If your wires from KIT-043 to microSD connector are too long, the signals will not be reliable for communication.
If you changed the GPIO pin assignments, then you may have used a GPIO that has a capacitor connected to it on KIT-043. Study the schematic in the KIT-43 guide. You may need to remove a capacitor, or re-assign the signal to a GPIO that does not have a capacitor attached to it.
Certain GPIO pins serve dual functions. Such as P4.0, P4.1. You may need to remove the option resistors if you're using GPIO dual purpose pins.
Good luck with your project.
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