It wasn't about opportunities, no, the household had no active band or instrument opportunities. I still can't get it to work in the world that my band household lives in, but it works fine in other worlds, both custom and EA-made, regardless of the number or type of LN venues (as long as there is at least one, of course). So sorry about the false alarm. 
No worries. I'm not sure exactly what is going on, because I don't know how many/which LN venues your neighborhood has. For example: If you only have a dive bar, and complete Ensemblely Challenged, then you won't be able to get any more opportunities. You'll still have that issue though with the "You already have a Skill Opportunity" message.
