Sim invisible except for the Plumbob?

If you are using a custom skin that can also cause the problem you are experiencing. I remember one time I download a Sim for TS2 and he was wonderful but when he would take a shower he would become invisible. It was the custom skin because he was a character from a movie someone had created. Not all skins play nice with Maxis clothes and or custom clothes. Also, just in case, custom hair and beards and other things can also cause this problem. Not all creators check and recheck their work. Last note there was an old bug about this but it was cleaned up in a patch so if anyone is using cds please make sure to patch the base, and all the EPs. The patches only patch their own particular EP. Also Family Fun stuff will need to be patched, too. M&G also was left with some bugs but MTS's Lord Darcy made some fixes for it years ago, since they never released a patch for it.

ETA: Also, just because a Sim is wearing a Maxis outfit doesn't mean there won't be a problem with it, if a person has some custom clothes that were created with that mesh as a totally separate outfit.