Hi

My N9 recently asks me to update to 40.2012.21-3.341.2 (update size: 0 KB) and it's the same version that I already have.
When trying to update there's an "update error" and the notification is still on the homescreen
Obviously, I've tried to update by Nokia Suite, but everything there is up-to-date and apt-get upgrade makes no difference.

How I can get rid of it without doing a reflash?

delete /etc/apt/sources.list.d/osa.list

(or, move it in a safe place)

The version number comes from the debian package version, so you can probably try the following:
- check with "apt-cache search mp-harmattan" what is the complete name of this package in your case (I guess something like mp-harmattan-341.2-pr)
- check the version with "apt-cache policy <name found above>"
If the 'Installed:' entry is different from 'Candidate:' entry, that may triggger the request to update. To avoid that you can trick the device that it has a 'newer' version like so:
- As root, edit the file /var/lib/dpkg/status (careful not to make mistakes, I suggest to make a backup copy of the file before beginning to edit)
- Search for a line that begins with "Package: mp-harmattan". Few lines below there is a line that begins with "Version:". Simply change that version number to something slightly bigger than what the update proposes, e.g. 40.2012.33-3
- Save the file and run "apt-get update" again