Quite strange - the links works perfectly fine for me, the page loads even though I'm not logged in. Alright here they are:
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BennyGirl613 : Letting a few sim hours pass or having them enter a rabbit hole *usually* fixes the issue. Hopefully EA will release a fix soon.
ParaParaParadise: I've had this issue too and have found that it's been fixed once the game has been restarted. Shouldn't be happening in the first place though.
Cyron43: Try this: Open the cheat line and enter resetsim FirstName LastName
whtrbt: I have found that putting him on the gym treadmill surprisingly fixes him. I have no idea why. But it's only temporary. Later on, I find that he can no longer do self interactions including the phone 
crinrict: [Just search Overwatch and ErrorTrap as we are not allowed to discuss them on the forums here]
The bogus steady gig is the issue here. (she earlier asked if the sim had any gigs going where the prioprieter had changed))
EDIT: I did just try the rabbithole solution and that did work. Don't know if the error would be coming back though. My Sim still has her bogus gig.
Stormkeep: Another "extreme" solution that might resolve it if that doesn't work is moving the sim out of their house and then back in from edit town.
And if that doesn't work, a last resort solution for me that fixes most any sim problem I've had. From Edit town, copy the household with house lot to the bin. Evict them, bulldoze the lot, and then place the binned copy back on the lot. The only thing that sucks about this, which is why I call it "last resort" is that you lose all of your relationship standings with sims not in your active household. On the other hand, with Showtime, that might be a good thing.
Finbaa: I have exact same problem!!! Something wrong with outfits this time...
Its not about gym for me... It works, when sim changes clothes....shower for example...
Someone also said that updating their graphics card drivers helped...
Let me know if any of these worked
