SD card single write block
As far as I'm aware, the correct procedure for a single-block write operation is:


Send CMD24
Wait for the 0x00 acknowledgement
Send 0xFE
Send entire block (512 bytes for modern cards)
Send 2-bytes of anything (or 2-byte CRC, if enabled)
Wait for xxx0yyy1 data response token
Check that yyy = 010


I have a suspicion that you're not waiting for the CMD24 acknowledgement before sending the data. That's what I did at first, too.

By the way, that output of sector 2001 looks suspiciously like a FAT FS Information Sector (which always starts with RRaA), which usually is located at block 1 of the partition. Does your partition start at sector 2000?