@Nici2468 The 64-bit version of Sims 3 is installed into Users > your username > Applications by default, with a Sims 3.app and a separate "The Sims 3 Packs" folder. Uninstalling a pack is as simple as moving its subfolder out of the Packs folder, but I wouldn't recommend removing an expansion mid-save as it can corrupt the save. That's true for this save and in general: removing an EP will leave stranded data in the save with no way for the game to resolve it.
What you can try is sending all the visitors home. I don't know how well this works in the University world, so be prepared to quit without saving and try again if this doesn't help the first time around. Install NRaas Register, if you haven't already, click on City Hall, select NRaas > Register > Tourists, and change these settings:
Allow Tourists: False
Chance of Leaving: 100
Maximum Number: 0
You may be able to help them leave faster by clicking on the tourists and selecting NRaas > MC > Basic > Go Home; you can run it from City Hall instead, by choosing MC > Sim > Basic.
You can also install Traveler, if you haven't already, and Pause Travel. This will (probably) prevent your active sims from being sent home right away, so you can give the game time to get rid of the existing travelers if the Register changes plus Go Home don't do the job alone. But that might throw off the schedule for the next University term, whenever you want to play it, so only use if if you absolutely need it. Once you unpause travel, your sims should be sent home at the appropriate time of whatever day that is.
Before sending your sims home, I'd recommend an MC town reset as well. And it's worth keeping all the performance-related settings you've already found, at least until you've fixed the issue.
@puzzlezaddict
Thank you for all the great suggestions! I was really hoping this would work but unfortunately, my game is still crashing ☹️ . I changed the tourist setting as you suggested, managed to force all of the 'out of town' sims home (they even appeared greyed out in my sims relationships panel), and did a MC town reset before my university sim headed home. Despite the problem sim having left town and the reset, the imaginary friend is still popping up as an error according to Traveller.
@Nici2468 Try to Totally Annihilate (NRaas MasterController) the imaginary friend, if it appears anywhere in the world. You may need to filter to Homeworld and choose your sim's homeworld. Once you've done that, click on City Hall and select NRaas > MC > Object Stats > Inventory, try to find the IF there, and delete it. You'll need the MC Cheats add-on for this option to show up. If the IF isn't under Inventory, try Not Inventory.
