Having an issue with RegEnumKey

I'm trying to get a list of all user keys under HKEY_USERS. I tried this and it didn't work:

$i = 0
$x = ""
$count = 0
While 1
$i = $i + 1
$x = RegEnumKey("HKEY_USERS", $i)
If @error <> 0 Then ExitLoop
MsgBox(0,"Diag","SubKey #" & $i & " under HKEY_USERS: ", $x)
WEnd

It actually increments properly but $x is empty on each iteration. Any ideas what I'm doing wrong?

Thanks!