There have been a few times where I've had a Sim preparing to do something but they just stand there as if waiting for the path to clear. They don't wave their hands around or complain or anything but they're also not doing anything.

There are two ways you can fix this.

1. Reset the Sim.
2. Return the Sim home.

The first way can be done through the Nraas Master Controller mod by clicking on the Sim and entering the 'Master Controller' option through 'Nraas'. Simply click on 'Reset Sim', it appears under the 'Advanced' option.
The second way can be done through the same way although it's under the 'Basic' option and then 'Go Home' instead.
The easiest option, and best option if you don't have mods, is by using the command bar cheats. Press [Ctrl+Shift+C] and then type in 'resetsim (first name) (last name)'.

Happy Simming!