Q: firmware file is not compatible

Try deleting the IPSW files and letting iTunes re-download them.

Mac OS X

 

iPhone	~/Library/iTunes/iPhone Software Updates
iPad	~/Library/iTunes/iPad Software Updates
iPod touch	~/Library/iTunes/iPod Software Updates
Note: The tilde "~" represents your Home directory.

 

Windows XP

 

iPhone	C:\Documents and Settings\[username]\Application Data\Apple Computer\iTunes\iPhone Software Updates
iPad	C:\Documents and Settings\[username]\Application Data\Apple Computer\iTunes\iPad Software Updates
iPod touch	C:\Documents and Settings\[username]\Application Data\Apple Computer\iTunes\iPod Software Updates
Note: To quickly access the Application Data folder, click Start, and then choose Run. Type %appdata% and click OK.

 

Windows 7 and Vista

iPhone	C:\Users\[username]\AppData\Roaming\Apple Computer\iTunes\iPhone Software Updates
iPad	C:\Users\[username]\AppData\Roaming\Apple Computer\iTunes\iPad Software Updates
iPod touch	C:\Users\[username]\AppData\Roaming\Apple Computer\iTunes\iPod Software Updates
Note: To quickly access the AppData folder, click Start, and then in the search bar type %appdata% and press the Return key.

If that doesn't do it and it isn't the exact error, maybe this is what you need to read -> 'Disk cannot be read from or written to' when syncing iPod or 'Firmware update failure' error when updating or restoring iPod