"The client version you are using is too old. Please upgrade at http://pidgin.im/" message is display when I'm trying to connect to the ICQ network using Pidgin 2.3.1 from portage. I did emerge --sync, but no newer stable ebuild of Pidgin can be found in portage.
I had the same problem with pidgin-2.3.1. I tried the unstable pidgin-2.4.2 and it emerges just fine, but when I start it I get the same error. Furthermore, now everytime I set my ICQ-Account to "Active" in the account window, it instantly gets deactivated. Same for pidgin-2.4.1. USE-Flags for Pidgin: "dbus eds gstreamer gtk ncurses nls perl spell -bonjour -debug -doc -gadu -gnutls -groupwise -meanwhile -networkmanager -prediction -qq -sasl -silc -tcl -tk -zephyr"
*** This bug has been marked as a duplicate of bug 230389 ***