After the NSU failed (stops after 33MB) I tried the Flasher 3.5.
Everything is clear, how to do it. http://wiki.maemo.org/Updating_the_firmware

Starting the flasher in the shell:
"flasher-3.5.exe -F RX-51_2009SE_10.2010.12-9_PR_COMBINED_MR0_ARM.bin -f -R"
brings a few line with %m. No further comment. No action at all, the program simply stops.
The same result is when the N900 USB is not even connected.

IMHO the problems starts when connecting the N900 (pressing "u"), Windows says it has found a new device but at the end, an error comes (hardware problems with USB device).
I tried also a laptop with XP, the same here. For me the flasher doesn't install properly the USB driver.

I have Windows XP. Also tried Vista bit still without any SP (will do the update as wiki says you must have SP2).

Conclusion: Flasher 3.5 is bugy !!
No way to update to process the update. Incredible !!
I cannot imaging that I'm the only one with that problem.

Sorry there is another thread about this but I couldn't find it again.

flasher-3.5.EXE ?? you should not be writing that :P !! will that help??

basically windows vista if not 64bits will solve your problem !!

Flasher works fine on all windows version EXCEPT 64bit ones.

It looks like you have not got the correct usb drivers loaded. Have you successfully connected your phone in mass storage mode?

Also was the phone turned off when you pressed the "u" and plugged in the usb lead?

It does throw a usb error but flasher still runs, you may have to wait for 30seconds though.

Also I think I change my boot to load unsgined drivers (win 7 32bit)

try this method !!

Dont connect your device unless i tell you to
go to run:
cmd
cd\program files\maemo\flasher-3.5
flasher-3.5 -F (RX.bin) -f -R

wait untill it shows suitable device not found !!

switch of your n900 HOLD U and connect the USB to some NEW USB PORT where it will INSTALL AND DETECT THE N900 AGAIN....

i guess it should work then !!

please REVIEW REVIEW REVIEW the method !! thank you

The flasher immediately closes, so it useless to start it and then connect N900. I think it stops because the USB driver is wrong. Same happens if N900 is not connected.
Of course I have plenty of installations on the PC from earlier Nokia phones (Ovi..). Maybe it conflicts.Therefore I'll try with another one.

Why mass storage mode ? The N900 bootloader (u button) has nothing to do with that, I believe.

With the NSU it's a question wether mass storage or PC Suite. Only in PC suite mode, the N900 is recognised. But as said, it starts transmission but then stops always at the same point.

shut down all nokia applications before doing it !! and if its still dont work try uninstalling all the usb ports from the device manager and start a fresh start !!

and then follow my steps !!

what os are u using btw?