That's because the software on 41xx family is not available for customer install. The software on this machine is available just for service tech's with NVM Access/SW Download Tool installed on the PWS.
Go to www.xerox.com/security.
Under Security Resources there is a Software Release Quick Lookup Table with links to the latest Firmware available.
Latest available is 062.121.001.04300
I hope this helps.
For xerox 7556, I am looking for the software version of 061.121.228.04700 or Later. However, I cannot find it on the Xerox website.
Any help in this regard would be highly appreciated.
All the best,