While trying to jailbreak iOS4 on your iPhone 3G with Redsn0w you might have encountered this error: Unable to recognize specified IPSW. This is a pretty common problem and it’s nothing to be alarmed about.
First of all, to fix the unable to recognize specified IPSW error you need to make sure that you are using the right version of Redsn0w, which in thise case should be Redsn0w 0.9.5b5-5. Follow the download links for Redsn0w 0.9.5b5-5 for Mac or Windows.
If you are still encountering this problem it could be that you are using the wrong version of iOS 4. Redsn0w 0.9.5 B5-5 won’t detect iOS4 GM IPSW. The usual reason for this confusion is that both the Goldmaster (GM build) and the 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. However Redsn0w 0.9.5b5-4 would only be able to verify the Final release of iOS 4 firmware, so you will need to make sure that you download it from a trustworthy source.
Another solution to the unable to recognize specified IPSW error is to make sure that when you are downloading the IPSW firmware you OPEN WITH… iTunes. DO NOT SELECT SAVE/SAVE AS because the firmware will not be opened and it will not be read on Redsn0w.
