I had to reinstall NitDroid to register WhatsApp again so I could use Yappari on Maemo. I used this to access the multiboot menu. I did all I needed to do, then rebooted, selected Maemo, and got this nice message:

I googled and searched here, and saw that I needed to reflash the kernel. So I did that, using the RX-51_2009SE_20.2010.36-2_PR_COMBINED_MR0_ARM.bin image (Latest Maemo 5 Global release for Nokia N900) and following the instructions to make the flasher only flash the kernel (flasher-3.5 -f --flash-only=kernel -R -F <firmware-image>)
It did its job, then rebooted the N900, and... nothing changed. It still gives me the same error if I try to boot Maemo.

Why? What to do now? I'd rather not lose my settings and apps and all by doing a full reflash.

Edit: ignore everything, I did it again and it's now working. Go figure. *blink*

Another question, then: why has it misbehaved like this after installing NitDroid?