[c-nsp] "IP addresses may not be configured on L2 links" FastEthernet interfaces

[Danny]

New Cisco 815. Four FastEthernet interfaces, and I simply would like to
configure an IP address on one of them, however, the following error message
is produced when I attempt to configure an IP address: IP addresses may not
be configured on L2 links.

I imagine this is a simple fix, however, I will post the whole configuration
if necessary. Is show running-config still the best or is there a public
mailing list friendly output?

Thanks,

...D