Update 9/15/2016: Seriously, if you are still using Rosetta Stone to learn languages...you ought to "go out" more into the WWW. There are far better and more accurate (Yes, Rosetta Stone's vocabulary is really faulty at times, I have native speakers proven it to me) learning tools out there now: e.g. duolingo, memrise, etc. And no, I'm not advertising for these latter ones, they are totally free anyway, no ads, run faster and easier than Rosetta Stone.
This error pops up saying database out of date.
* find the tracking.db3 file in your appdata folder (for windows 7 its C:\programData\Rosetta Stone\tracking.db3 (hidden folder) and rename it to tracking.db3.bak
* Restart the pc
* launch rosetta stone (all your progress has been lost now)
* close the rosetta stone application
* rename tracking.db3.bak to tracking.db3
* Launch the application again and here you go, you can use it again
For error code 2123:
Solved by simply reboot, and reboot, and reboot, until it is fixed.
BTW, adding a line in the file dynamicStoredPaths.xml, next to tracking.db3, may help:
Line added to second last line of file, before </installerDefaults>.