Alot of us have faced this problem, after downloading a .dmg file from Safari, it shows a Disk Mounting Failed error messsage or a error -199.
This can be corrected using the disk utility tool under Apps->Utilities by going to Repair disk permissions or if you use Safari then Stop or pause during the download, causes this error.
I know its strange butyou may use ‘speed download’ – download manager for mac instead if you feel you’ll have to resume it.
Avoid stopping the download mid-way or better still ditch Safari 
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