I'm trying to make an iconset for an application, but keep on getting an error when I make it: `Hexchat.iconset:error: Failed to generate ICNS.`

I tried both exporting .png files individually from Illustrator, as well as using a script. Current script with a 1024x1024 png file as `Hexchat_8.png` is:

```
mkdir Hexchat.iconset
sips -z 16 16     Hexchat_8.png --out Hexchat.iconset/hexchat_16x16.png
sips -z 32 32     Hexchat_8.png --out Hexchat.iconset/hexchat_16x16@2x.png
sips -z 32 32     Hexchat_8.png --out Hexchat.iconset/hexchat_32x32.png
sips -z 64 64     Hexchat_8.png --out Hexchat.iconset/hexchat_32x32@2x.png
sips -z 128 128   Hexchat_8.png --out Hexchat.iconset/hexchat_128x128.png
sips -z 256 256   Hexchat_8.png --out Hexchat.iconset/hexchat_128x128@2x.png
sips -z 256 256   Hexchat_8.png --out Hexchat.iconset/hexchat_256x256.png
sips -z 512 512   Hexchat_8.png --out Hexchat.iconset/hexchat_256x256@2x.png
sips -z 512 512   Hexchat_8.png --out Hexchat.iconset/hexchat_512x512.png
cp Hexchat_8.png Hexchat.iconset/hexchat_512x512@2x.png
iconutil -c icns Hexchat.iconset
rm -R Hexchat.iconset

```

Every time it is the same, though, with or without an output file:

```
iconutil -c icns Hexchat.iconset
Hexchat.iconset:error: Failed to generate ICNS.

iconutil -c icns Hexchat.iconset -o hexchat.icns
Hexchat.iconset:error: Failed to generate ICNS.

```

chmod'ing and/or sudo doesn't work, and the man page shows no option for verbose error output. What am I doing wrong?