Occasionally 3 lights of death with 0020 & 0021 errors

[proconsoles]

I got a Xbox360 with Hitachi 46DH drive, from which the controller board was defective.
I put the controller board of a V59 in it, flashed it with the procedure:

1) I installed the new V59 controller board, and did:
restore.bat d
to make sure the original firmware is there

2) Then I dumped the firmware of the V59 controller board.
memdump_win d 12200 8 8000 orig59.bin

3) I started "360FW-Toolbox-31B-Repack" by double clicking "360FwTb".

4) I opened the original firmware from the CD-R in order to get the key, which need to be placed in
the firmware. I clicked on ... next to "Open a Firmware File First...", and opened original.bin from the CD-R.
Then I copied the key, and put it in Notepad

5) I restarted Toolbox, and opened previously dumped orig59.bin
Replaced the key with the key, that came from the firmware on CD-R
- then clicked on the button "Replace Key"
- then clicked on the button "Generate Encrypted File..."
The firmware was written as "orig59-e.bin".

6) Then I wrote the firmware to the V59 controller board with:

flashsec_win d orig59-e.bin 90004000 1000

7) Then I ran from GaryOPA 2.4 :
flash24s.bat d 280507

It is working, and backups play fine.
But occasionally I get the 3 lights of death, with the error codes 0020 and 0021 :

0020 (Not yet known, possibly overheating)
0021 DVD Drive Time out - Can be caused by problems with a firmware flash. This is also speculated to sometime be caused by a problem with the southbridge chipset on the motherboard.

What do you think is the cause of this ?
And, maybe you know a solution ?