How long are you having this problem?
And have you installed Showtime? The last one I'm asking because I haven't heard of this problem before the arrive of this expansion so it could be some connection between the two that is not smoothly working.
I've removed my previous message becausedue to some bug my phone didn't finish my post so it came through only half.
I've adviced you it could help if your Sim has been introduced to the Sim you want to interview as some functions are prevent until the moment your Sim has introduced him or herself, but I now don't think this will solve anything in this situation.