Problem: You can place the object in Build or Buy Mode, but when you switch into 'Live' mode, the object disappears

Reason: This issue is caused when an installed object requires an expansion pack which you do not have installed. Each object which is based on an item that came with one of the Sims expansions has a code within the object's behaviour that tells the object to remove itself if a particular EP is not present in the user's installation.

Sadly removing that code doesn't fix the problem, it is there as a safeguard to help prevent your game becoming corrupted because the object needs global commands included in a particular expansion but missing in the basic game, in order to function correctly.

If you particularly want to have the object then I'm afraid the only real solution is to buy and install the expansion pack it needs. The object shouldn't cause any particular harm to your game if left in your game folders, however for the sake of not taking up unnecessary space on your hard drive and irritating you every time you see it in your game catalogues, it is probably advisable to delete the .iff file from your game folders.