cheat command not working

The problem you describe has nothing to do with custom content.

It is occurring because there is some other program on your machine which uses the same keymix as does opening the cheat box.

I have no way of knowing what programs you may or may not have installed on your computer -- you'll just have to see if yo can track down the culprit.

From the Wiki:

"Don't Have Cursor XP?
Then you have another program that uses that same key combination. Try thinking of what you've installed recently, since the cheat console stopped working. If you can't remember, or if it's never worked, check your running programs (the list of icons showing beside your computer clock). Open them and look at their settings or preferences to see if there's an area where you can set keyboard shortcuts. One of them has CTRL-SHIFT-C as its shortcut and you should change it to something else, or shut it down, before running The Sims 2."

I don't use Vista, but seem to recall hearing that it comes installed with some program with the word Health in its name which also uses the Control-Shift-C key combo.

You can try this as a workaround - it may or may not work in any individual situation:

Instead of just Control-Shift-C, press Control-Shift-Windows Key-C