Error 0xe00002c9- Disk images failed to mount

I have a recent problem, everytime I download a program with a .dmg file (such as the newest version of stuffit) I receive an error saying that the following disk images failed to mount. I've had this problem with various other programs I've tried to download recently. Can anyone tell me what this means and more importantly how do I fix it? Because none of my software updates will install. Oh, they'll download but whenever I try to open it after its downloaded it won't.I've never had this problem before, and like I asked before how do I fix this?