What is causing character replacement?

[Gadget_Guy]

I just noticed on my site that characters are being replaced.

Example:

but I’m sure there

That should be "I'm sure there"

Where can I look to fix this?

D.

[ozzy47]

Have you tried on a unmodified default style?
Have you tried with all mods disabled?
What vB version and PHP version are you running?

To temporarily disable all mods, edit includes/config.php file and add this line right under <?php add the following.
define('DISABLE_HOOKS', true);

So it looks like this:
<?php
define('DISABLE_HOOKS', true);
/*================================================= =====================*\
|| ################################################## ################## ||
|| # vBulletin 4.2.2

Use notepad++ (http://notepad-plus-plus.org/download/v6.6.8.html) to edit any files.