After upgrading C2501 IOS, arrow keys act strange

[CCNA2]

Hi, I have a Cisco 2501 router with an IOS (IGS) image version 11.0. When I upgrade to a newer image (a C2500 image) The arrow keys produce what appears to be breaks (ctrl+break). About 3 breaks each time I press an arrow key. I have tried with 2 different images, a version 12.0 and a version 12.1. When I restore the original image there is no problem. I have tried erasing the NVRAM and that didn't help. Is it because the original image is an IGS image (< 11.2 Version)?

Original image name: igs-in-l.110-18.bin
New image names: c2500-i-l.121-2.T.bin, c2500-is56i-l.120-24.bin

Here is the &quot;show version&quot; output:

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Cisco Internetwork Operating System Software
IOS (tm) 3000 Software (IGS-IN-L), Version 11.0(18), RELEASE SOFTWARE (fc1)
Copyright (c) 1986-1997 by cisco Systems, Inc.
Compiled Mon 01-Dec-97 18:11 by jaturner
Image text-base: 0x0302186C, data-base: 0x00001000

ROM: System Bootstrap, Version 5.2(5), RELEASE SOFTWARE
ROM: 3000 Bootstrap Software (IGS-RXBOOT), Version 10.2(5), RELEASE SOFTWARE (fc
1)

Router uptime is 26 minutes
System restarted by reload
System image file is &quot;flash:igs-in-l.110-18.bin&quot;, booted via flash

cisco 2500 (68030) processor (revision A) with 16384K/2048K bytes of memory.
Processor board ID 01198132, with hardware revision 00000000
Bridging software.
X.25 software, Version 2.0, NET2, BFE and GOSIP compliant.
Cisco-ET Extended Temperature platform.
1 Ethernet/IEEE 802.3 interface.
2 Serial network interfaces.
32K bytes of non-volatile configuration memory.
8192K bytes of processor board System flash (Read ONLY)

Configuration register is 0x2142

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I hope someone can help me.

Thanks.

Thomas