I had just bought 2 Xbee S2C and was trying to configure it as Coordinator and Router via the XCTU software. After my xbee got scanned and I added the device, I tried to configure it -but got an error saying that “A firmware could not be found for the selected device”. So I tried to update the radio firmware library, but that too gave me errors. All the errors that I have encountered can be found in this link - https://imgur.com/a/zukLjcZ.
The firmware version you are looking for is very old (2012). You really should be using the XBee recovery and install the current version for the XBee S2C hardware which is 4061.