Haha, let me guess, you’ve downloaded a mac image file, but its an img, not an iso. Well, no matter whether I’m right or wrong, I have the same problem. If I run across anything I’ll post here again…

I came across this because I had to burn an img file from my mac using my windows laptop wich has dvd burner.

Open the disk utility in your mac.
2. Drag the disk image into the left-hand pane (where all your drives are listed) of Disk Utility.
3. Click on the file you just dragged into Disk Utility (should appear in the left-hand column).
4. Click on the ‘Images’ menu, then choose ‘Convert…’
5. When the ‘Convert Image’ dialog pops up, select ‘DVD/CD Master’ from the ‘Image Format’ pop-up menu.
6. Name your file, with ‘.cdr’ at the end of the filename, then click ‘Save.’
7. Disk Utility will convert the file to an ISO image. After this finishes, replace the ‘cdr’ at the end of the filename (in the Finder) to ‘iso’.
8. Now, the disk should be burnable on a Windows PC (simply copy the file to your PC by either copying it across a network or using some other means of transferring the data).

Holp it helps.

Great!