UIPEthernet and Twitter

Hi,
I was trying to interface arduino with twitter by using ENC28J60 and the library UIPEThernet.H

I have included the library

twitter.h
UPEthernet.h
SPI.h

but I always got the following errors:

\Twitter/Twitter.cpp:60: undefined reference to EthernetClient::connected()' \Twitter/Twitter.cpp:63: undefined reference to EthernetClient::read()’
\Twitter/Twitter.cpp:62: undefined reference to EthernetClient::available()' \Twitter/Twitter.cpp:64: undefined reference to EthernetClient::flush()’

the only way to run the program is to include Ethernet.h but I have the ENC28J60 thus the UIPEthernet.h is needed.

Any suggestion on this?

M