I remember Mootilda answering that over in sims 2 help at MTS a while ago... The exact answer may have been archived by now but I'll see if I can find it and link you to it.

Edit: Searching for the post showed no results. I sent her a PM to ask if she could come here and repeat her answer.

Thanks for the heads-up, Ghost.

First, try the magic wand: http://www.moreawesomethanyou.com/ffs/al/hacks/magicwand.zip. It comes with its own collection file. Take the box from the collection and place it anywhere on your lot. Then delete the box and save the lot.

If that doesn't work, this solution should work for any sim stuck on any non-home lot.

1) Backup your save game now, just in case this doesn't work.

2) Run SimPE and open your neighborhood. Be patient; it may take a while.

3) Select Family Information (FAMI) in the left pane. Again, please be patient while it fills the right pane.

4) In the right pane, select a family which lives in the same neighborhood as the family that you are trying to retrieve.

5) Look at the Plugin View in the bottom pane.

6) Write down the Subhood number in the Plugin View.  We'll need this later.

7) Select your lost family in the right pane.

8) Look at the Plugin View in the bottom pane.

9) If the "Now on Lot" field is not equal to the "Lot Instance" field, then copy the "Lot Instance" and paste it into "Now on Lot" (see notes below).

10) If the Subhood number is not the number that you wrote down in step 6, change it.

11) Commit, save and exit SimPE.

12) Run the game and see whether the family is available. If not, restore from your backup.

Notes:

1) To copy a field, select the entire value, then hold the key down and type C. This will copy the value to the clipboard.

2) To paste a field, select the entire value, then hold the key down and type V. This will paste the value from the clipboard, overwriting the existing value.