Electronic – Problems reading data from a microSD card

I am trying to read a block of data from a standard capacity micro SD card, but the received data does not make any sense. Here is what I'm doing:

• Initializing the card
• Reading data
  • Setting CS low
  • Sending CMD16 to set block length
  • Sending CMD17 with start address
  • Waiting for start byte (0xfe)
  • Receiving bytes and printing them to the serial terminal
  • Receiving CRC
  • Setting CS high
  • Sending 8 extra clocks (?)

The data I'm trying to read is the FAT16 boot sector, as shown below:

And the data I'm getting out is this:

At this point, I can't even begin to think of what is going wrong. I don't think it's a transmission error, because the data out is always the same. I can also read the boot sector signature 0x55 0xAA every time, even if I set the start address to 510 and read two bytes, they come back perfectly. The problem is that I can't read other bytes.

I also tried swapping cards and that didn't help either.

What am I missing?

EDIT: the function in question is below.

bit sd_read_block(unsigned long size, unsigned long start_addr)
{
    unsigned long i;
    unsigned char r;

    SD_CS = 0;

    r = sd_card_cmd(16, size, 0);

    sprintf(usb_uart_tx_buffer, "CMD16 R Token: %02x.\r\n", r);
    usb_uart_tx(usb_uart_tx_buffer);

    r = sd_card_cmd(17, start_addr, 0);

    sprintf(usb_uart_tx_buffer, "CMD17 R Token: %02x.\r\n", r);
    usb_uart_tx(usb_uart_tx_buffer);

    // wait for start token
    r = 0;
    while (spi_rx_byte() != 0xfe) {
        if (r++ > 25) {
            SD_CS = 1;
            return r;
        }
    }

    for (i = 0; i < size; i++) {
        if (i % 20 == 0) {
            UART1_TX(0x0d);
            UART1_TX(0x0a);
        }
        sprintf(usb_uart_tx_buffer, "%02x ", spi_rx_byte());
        usb_uart_tx(usb_uart_tx_buffer);
    }

    // CRC
    spi_rx_byte();
    spi_rx_byte();

    // extra clocks
    r = spi_rx_byte();

    SD_CS = 1;

    return 0;
}