If I were you I would ignore the dmg problem until you fix the higher priority problem of the disk errors. Maybe fixing that will fix the dmg problem and I'm guessing almost certainly the spinning cursors.
Oct 24, 2019 Mac mini introduced in early 2009 or later iMac introduced in mid 2007 or later Mac Pro introduced in early 2008 or later Xserve models introduced in early 2009. To find your Mac model, memory, storage space, and macOS version, choose About This Mac from the Apple menu. If your Mac isn't compatible with OS X Yosemite, the installer will let.
As I understand it Lion drives are formatted with a special 'recovery partition' which takes the place of the separate bootable installation disks. It contains a copy of Disk Utility. Read the following on how to use this partition.
Dmg File Mac
Mac Dmg File Won& 39 1
By the way, if you are using Lion you should update your sig.
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Dec 12, 2011 10:58 PM