This is still a problem for me as well.
I did not know it was because of groups in festivals! That's why I never can choose my sims friend to sing duets! Good to know the reason, but it would be good to have this fixed.
I also experience this since the release of City Living. I guess it is because the game thinks the festivalgoers are alrady in an active situation and thus are not allowed to join the karaoke duet situation.
It is still bugged. Any solution for this? A mod or something since it seems EA has no intention to fix it?
@babuchas01 Check the pinned thread at the top of the Bug Reports forum titled Common Game Fixing Mods, and scroll down. Look for the link to karaokeduetfilterfix by Bienchen. I've had that mod/fix installed for several months at this point and it seems to work perfectly.
