According to Cisco docs the WIC-1ENET does NOT auto-sense ( amazing .. ):
formatting link
try setting the speed to 10 and the duplex to full to see if the cable modem support it
send some traffic and then check the output of show interface for runts and giants whci is one sign of duplex mismatch.
IOS Commands
This section describes the full-duplex and half-duplex IOS commands. Cisco WIC-1ENET is set to half-duplex mode by default, and it does not auto-sense. If you set the Cisco to full-duplex operation, you must also set the device to which the port is attached to full-duplex mode. full-duplex Command
To put the Ethernet interface into full-duplex mode, use the full-duplex command. The "no" form of this command changes the port to half-duplex mode.
full-duplex no full-duplex
Syntax Description
full-duplex
Interface is in full-duplex mode.
no full-duplex
Interface is in half-duplex mode.
Default
Half-duplex mode
Command Mode
Interface configuration mode
Usage Guidelines
Use the full-duplex command to put the Cisco WIC-1ENET Ethernet interface into 10-Mbps full-duplex operation. The interface can be put into half-duplex mode again by entering the no full-duplex command.
Example
The following example puts the Cisco WIC-1ENET Ethernet interface into full-duplex mode:
1750(config)#interface Ethernet 0
1750(config-if)#full-duplex
The following example puts the Cisco WIC-1ENET Ethernet interface into half-duplex mode:
1750(config)#interface Ethernet 0
1750(config-if)#no full-duplex
To verify the interface state, enter a show interface command as follows:
1750#show interface Ethernet 0
Ethernet0 is up, line protocol is up
Hardware is PQUICC Ethernet, address is 0001.64ff.ef6a (bia
0001.64ff.ef6a)
MTU 1500 bytes, BW 10000 Kbit, DLY 1000 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation ARPA, loopback not set
Keepalive set (10 sec)
Full-duplex, 10BaseT
....