Icon files appear jagged/pixelated on PC

I'm having an issue with a set of ico files I've created for a client. I'm working on Mac OSX and the icons look great when I open them. However when my client opens them they appear jagged or pixelated. (I've attached an image). He's working on a PC with Windows 7.

To give you my process of creating these: I created a set of 64x64, 32x32, and 16x16 pngs in photoshop and I used an online icon converter/generator to combine the different sized pngs in a single ico file.