I see that you are still running version 7.5.5, released February 10th, 2010
It looks as though your issue could be caused by database charset collation issue. Have you recently changed your database structure. It could also relate to if your web host has updated their MySQL or PHP versions lately.
I say this especially because I am able to use that character in my post to your site, and preview it, before posting it to your database. (see attached screenshot)
Have you also recently changed from "utf-8" to "iso-8859-1" ?
In addition, I noticed that your page header has several errors in it, which could also cause page display issues.
UNRELATED: Please use a NSFW tag on your link, since it does contain photos of women in string bikinis.