Tried this and got income like normal...
Maybe you have changed something in your game that causes this.
I'd say check the config file and look what multiplier you got on income fro working in a brothel. If thats not the case, have you checked if the girls really worked or did they refuse to work, or any other factors that could be affecting the girls, like that they just didnt get any customers that shift.
If nothing works, I'd suggest to download the game again.