Need help with hdiutil - "Attach Failed"

[LoneWolf121188]

So here's what I'm trying to do: take an .iso, convert it to a read/write image, add some files to it, then burn it. Here's what I've done:

• Used hdiutil to copy the image (we'll call it Image) to a -rwx image (we'll call it Imagerw)
• Changed the permissions with chmod to -rwx (for some reason it didn't automatically do that)
• Copied the files/folders that I needed to the image

Now I'm stuck. One of the problems is that I can't actually see the image in Finder. I see it in /MY_NAME/Volumes, along with my Macintosh HD and Windows partitions on my HDD, but it's not under the Devices dropdown in Finder, nor does it show up in Disk Utility. I tried using "hdiutil attach /Volumes/Imagerw", but then I get "hdiutil: attach failed - Operation not supported on socket". Same if I try hdiutil burn /Volumes/Image/. Help?