Sometimes the telepathy processes hang and therefore any connection attempt to IM services fails with network error. This can be solved by either restarting or killing the appropriate processes:
* telepathy-gabble for Facebook, GTalk, Jabber, OVI
* telepathy-haze for Yahoo!, ICQ, AIM, MSN (Haze), libpurple
* telepathy-sofiasip for SIP
* telepathy-butterfly for MSN
Then try connecting again.