Earlier we posted a tutorial on how to jailbreak iOS 4 on iPhone 3G with Redsn0w 0.9.5. While the tutorial seems to work just fine, a couple of users have reported to have encountered an error.
The error, which says "Unable to recognize specified IPSW" keeps popping up whenever a user tries to browse the iOS 4 firmware file from Redsn0w 0.9.5.
There are two solutions to fix this error. Number 1 is to make sure that the right build of Redsn0w is being used, which in thise case should be Redsn0w 0.9.5b5-5. Download Redsn0w 0.9.5b5-5 for Mac or Windows
Number 2 is to make sure that the right build of the iOS 4 firmware file is being used for iPhone 3G. There may be a confusion here since both the Goldmaster (GM build) and Final release use the same build number so filename for both builds would be the same i.e. iPhone1,2_4.0_8A293_Restore.ipsw but Redsn0w 0.9.5b5-4 would only be able to verify the Final release of iOS 4 firmware so make sure to download it from a verified and trustworthy source. Here we have verified iOS 4 firmware file download links for all devices.
That's it! all it takes is a bit of research and common sense. Good luck!