What is the highest general release version of Cisco IOS that the 1720 router below will accept? I've put a show version below. I've tried c1700-y-mz.123-23 but it tells me there is not enough memory. When I try to look at the readme files on Cisco's website for the various versions it tells me the Readme files are "Forbidden" even though I am using my Cisco logon ID so I can't look it up myself. I understand why they won't allow download of firmware but I don't understand why they won't let me view a readme file. Thanks for the help!
Cisco Internetwork Operating System Software
IOS (tm) C1700 Software (C1700-Y-M), Version 12.0(7)T, RELEASE SOFTWARE (fc2)
Copyright (c) 1986-1999 by cisco Systems, Inc.
Compiled Mon 06-Dec-99 14:14 by phanguye
Image text-base: 0x80008088, data-base: 0x805994D8
ROM: System Bootstrap, Version 12.0(3)T, RELEASE SOFTWARE (fc1)
pdc-rtrgolf uptime is 1 hour, 33 minutes
System returned to ROM by power-on
System image file is "flash:c1700-y-mz.120-7.T"
cisco 1720 (MPC860) processor (revision 0x501) with 18432K/6144K bytes of memory
Processor board ID JAD042106MZ (3718208237), with hardware revision 0000
M860 processor: part number 0, mask 32
X.25 software, Version 3.0.0.
1 FastEthernet/IEEE 802.3 interface(s)
1 Serial(sync/async) network interface(s)
32K bytes of non-volatile configuration memory.
4096K bytes of processor board System flash (Read/Write)
Configuration register is 0x2102