IE9 - CSS3111: @font-face encountered unknown error

I found this answer, which addresses the question more directly than the accepted answer, which really, shouldn't have been the answer :)

And now to our main highlight - the "CSS3111: @font-face encountered unknown error". This error is very ambiguous. If you have a look at MSDN again, you'll see its description says: "An unknown problem was encountered with the "Web Open Font Format (WOFF)", and "Embedded OpenType font (EOT)" of the Cascading Style Sheets (CSS) font". "Unknown Problem" doesn't sound too good to me - how am I supposed to solve an unknown problem? Fortunately we're given a hint here. It says: "Check source of the fonts". Indeed, CSS3111 is usually caused by an issue with the font's binary source. One of the popular online TTF to EOT converters for example produces EOT files with a NAME table that doesn't comply to the Microsoft standards, which results in EOT fonts that never load in IE and produce the CSS3111 error. So, when you experience a CSS3111, it is always good to try using a different TTF to EOT converter or font face generator.

Source: http://www.marinbezhanov.com/web-development/16/how-to-embed-webfonts-properly-and-how-to-solve-the-ambiguous-css3111-font-face-encountered-unknown-error/

I solved the problem on IE 9 using the below @font-face:

@font-face {
    font-family: Gidole;
    src: url('Gidole-Regular.woff2') format('woff2'),
         url('Gidole-Regular.woff') format('woff');
}