Was working on my site (in development) on Joomla 2.5.8 and upgraded to Joomla 2.5.9. That is where I found out that Ninjaboard com_ninjaboard_v2.0.3Beta.zip may have a bug in Joomla 2.5.9.
Because I was not 100% if the error may have been in my migrated users/website I reproduced a similar, yet 100% clean setup with approximately 200 Joomla users.
The problem is, NinjaForge is only showing a portion of the users as you can see in this screenshot:
Another problem is importing. None of the importing features work. Hopefully this is still in the works?