Friday, November 14, 2008

Error 4960 and Codec Overruns; Can't Open .dmg Files

I've been having a problem opening .dmg (disk image) files that I downloaded at home recently. I can download the same files on the same computer (MacBook, of course) at work so I knew it wasn't a problem with the computer.

I would download a file from the internet at home and the download would look normal. As I opened the file, however, the problem would manifest itself as follows:
  • I initially got a 4960 error code which typically means a corrupted disk image.
  • After about 2 weeks of that, the error code changed to Codec Overrun.
It was hard to find anything related to these problems on the web which is the main reason for this post. I hope that this gets indexed to help anyone else suffering the same problem.

Well, I found the problem but I'm not sure of the cause. The problem turned out to be caused by the SPI Firewall that's built into my router. Evidently, the firewall was corrupting files.

Everything has been working well since I turned off the firewall.

Now a couple of words of warning. The SPI (Stateful Packet Inpection) Firewall protects your LAN against Denial of Service attacks. This should only be disabled in special circumstances (or so my router software tells me). This is the router at my home so I'd be pretty unlucky to suffer from such an attack. I'd think twice if this was my business router.

Turning off the firewall also cured another problem I've been having. I was having a problem watching some embedded videos (not all, just occasionally). That problem also seems to have been cured.

I still don't know what caused the problem. It may be something my ISP changed (they've been doing some work around here recently). It may be time to replace my router (it is 4 years old and on all the time). It might be a change in the Mac OS (recent update to 10.5.5). I'll post again if and when I find out more.


Nishant said...

Does this mean that if I do not have internet connection then I can not use .dmg file? I have a .dmg file which was working earlier but now suddenly doesn't seem to be working. Only the change is that I have moved the .dmg file to different location just for backup purposes. I agree to the post which says that it is file IO error on Mac.

diegoferrari said...

Same problem as Nishat Here. The file was working and it's not anymore. estrannnge! have just moved the files to another folder and kaboom!
The copies of this files have the same -4960 error...
the bizarre is that i have opened the file before moving and it was ok... than moved, opened again and error. = P

Anonymous said...

IF you have the files saved on an external drive (or even if they were at ANY point saved on an external drive), go to your manuf's website and download the latest firmware upgrade for that external drive. Worked for me and solved ALL my .dmg issues, ALL my public movie atom issues, and all my "Error 4960" issues.

If the files became "corrupt" at some point (while they were on an external drive) - copying them to another location would only be making copies of broken files. You have to go back to the drive (hopefully they are still there). Keeping the files ON the drive, update the firmware. Everything came back for me, instantly. Whew!