Okay, I found something really interesting... it works fine on PHP5, but not on PHP4. Or, perhaps it works fine on Windows, but not on FreeBSD.
I uploaded my Wingdings 2 TTF file in hopes that it would work for you, knowing that they worked for me. Then, I uploaded my test file--and, low and behold, I get the same error as you.
Works under PHP5 on Windows XP, doesn't work under PHP4.3.5 on FreeBSD.
So, apparently you're not alone with this.