Acer Veriton V66LT-4 with. Pentium 3 Coppermine 800

[Sandfish]

Hello all together,

after weeks of struggeling I guess that I have to surrender. I got an old Acer Veriton FP monitor computer as a gift from a friend a few weeks ago. Usally I'm trying to configure old computers with its maximum of RAM and CPU.

So the original CPU was an Intel Pentium 3 600MHZ (SLOT1, SECC2) and I wanted to replace it with an Intel Pentium 3 800MHZ (SLOT1, SECC2). The computer boots with the new CPU but hangs with the message "CPU Update BIOS Code Mismatch". It is not possible to skip this via key stroke.

The board that is assembled is an Acer Veriton V66LT-4 that sometimes also was assembled in Siemens Scovery 250 computers. I downloaded the newest bios from here
and flashed it but the board still says "CPU Update BIOS Code Mismatch".

So I guess I have to update the microcode manually. I downloaded a microcode file from intel although it is not written that the 800MHZ Coppermine is included. When watching it in a hex editor it seems to include more than the few listed CPUs.

I tried it to flash the microcode with the ctmc tool from the German computer magazine c't but after hours of loading the Intel dat file [and nothing happend] I turned of the computer.
I hope you can help me to update the microcode of this board because I don't have any ideas left. Last time you successfully helped me with another board so I'm confident that you can help me.