Cisco WAN :: Lab Router 2500 Configuration Not Working

I grew tired of entering my username and password in my 2500 series lab router. So I removed authentication by typing "no username xxxxxx  password xxxxxx".Different than what I expected (removal of authentication), the router still prompted me for my username, it just won't accept anything I type. 
 
I decided to do a password reset, I changed the register to 0x2102 and then typed "i" for Initialize.   It comes back with error "Configuration from version 12.0 message may not be understood correctly."   and then boots to running config with a prompt for username again....right back where I started.
 
why removing authentication by just typing "no username xxxxx password" would lock me out?If I am actually locked out or maybe there is another way to access?