It's happened to me a few times too. I think this thread is full of solutions to this problem.
Well the issue is originally caused (aside from the cluster of code screw ups with all the receptionists anyway) by trying to force the issue with Kari and Mallory at the very first interaction with Lois regarding more/new staff. This will 100% cause this error. Why people would go against Lois' recommendations is a mystery. However, that does not excuse the code,...which I believe is actually fixed now (it used to originally crash the game at the point years ago).
Second thing that will cause this error is not chatting up Vanessa in London. That part of the code where it checks variables for available potential staff still has not been fixed. Last and final thing that can also contribute/add to this annoying error, is giving Aria a job as soon as you can (as this removes her from the potential pool later).
One can argue, it takes a series of decisions to cause this and how likely actually is this? The problem, as a VN dev, is coding your VN to anticipate literally every single choice you have allowed and people making choices that are extremely unlikely. Even if one person in twenty thousand takes a weird series of decisions...you need to account for that.
Togs unfortunately, does not...or just (as I have said before) is not skilled enough to. He has a lot of good ideas but they are so badly implemented as what he actually wants to do, is beyond his current skill set. That's not attacking him personally, this is my 8th most posted in thread...I love this VN but loving it/being a fan and
not being blind to all it's coding issues and errors are not mutually exclusive. One can do both.