Core issue
The error message appears if line vty is configured with transport input ssh.
When line vty is configured with transport input ssh, then HTTP access is restricted. This is a known issue in Cisco IOS Software Release 12.2.
Resolution
As a workaround, enable transport input all as this example shows:
Hostname(config)#line vty <0 15>
Hostname(config-Line)#transport input all
As an alternative to this workaround, you can also upgade to Cisco IOS Software Release 12.3 or later in order to resolve this issue.
Go to the Software Center in order to download Cisco IOS Software Release 12.3 and later.