download RX-51_2009SE_10.2010.13-2.VANILLA_PR_EMMC_MR0_ARM.bin
and
RX-51_2009SE_20.2010.36-2_PR_COMBINED_MR0_ARM.bin

then flash the EMMC FIRST with command
and as soon as it finishes
(the commands have to be on ONE line, obviously...)

this should provide you a factory grade software configuration.
personnaly, i find it less cumbersome to do that whenever something goes wrong & then restore my settings (& installed programs) from a backup (the safe in the application menu; this requires of course that you either make the backup on a mSDHC card of copy it off the EMMC before re-flashing it & put it back afterward)
then using backup_menu; tried it once but somehow didn't work out for me
and it's not like i'm not "reflashing" my OSes on my PC(s) routinely with partimage or FSARCHIVER

nota bene: backup does not save your programs, it only saves the list; restoring them requires a network connection (preferably Wi-Fi, obviously) so that the latest versions can be downloaded anew...

EDIT: the errors about missing dependencies you got when trying to install b-m probably came from that you tried to install it from the link provided in the post; you need to add the repositories (catalogs in NOKIA's parlance); @ least extra-testing (and if you are not easily scared... dev )
go to this page with your N900 (there are links to install the catalogs automatically)
http://www.nokiadistrict.com/reposit...or-nokia-n900/