Can't load images in GuiMainMenuBitmap

I'm going through the bitmap tutorial and when it ask you to load the bitmap for the main menu I click on the option to load in a bitmap but it wont let me select any of the images, they have a .png extension and .jpg are grayed out as well. I restarted the project thinking I might have selected something else but it still won't let me load in any of the images in. I'm working on a mac and that's when I'm having the problems but everything works fine on my pc. Thanks.

Craig