Just playing with my 2600 and try to upgrade IOS to support 3DES in order to test IPSEC/VPN connexion and got some kind of message like that :

%Error opening tftp://255.255.255.255/network-confg

%Error opening tftp://255.255.255.255/network-confg

To disable it:

VPN-CLI#c
Enter configuration commands, one per line.  End with CNTL/Z.
VPN-CLI(config)#no ser
VPN-CLI(config)#no service ?
  alignment              Control alignment correction and logging
  compress-config        Compress the nvram configuration file
  config                 TFTP load config files
  dhcp                   Enable DHCP server and relay agent
VPN-CLI(config)#no service config
VPN-CLI(config)#^Z
VPN-CLI#wr
Building configuration...

*Mar  1 00:32:37.568: %SYS-5-CONFIG_I: Configured from console by console[OK]
VPN-CLI#