After upgrading Pidgin and Sipe on Debain wheezy I came across:
Failed to authenticate to server
Desipe my password having not changed.
It turns out you need to disable “Use Single Sign-on” in the Advanced properties.
The Sipe plugin’s website has a good FAQ dealing with problems therein: http://sourceforge.net/p/sipe/wiki/Frequently%20Asked%20Questions/
In Debian Wheezy, you can install the Lync / Office Communicator / Sipe plugin for Pidgin.
But, even with the correct login information you get a Read Error when trying to connect.
You need to set an environmental flag before running Pidgin to overcome this. Here’s a script that does it:
export NSS_SSL_CBC_RANDOM_IV=0 pidgin