The 2.6.1 version (portable and not) has a bug that will prevent proper connection to XMPP service (jabber to some).
This is mentioned in bug #9956 at (http://developer.pidgin.im/ticket/9956).
The fix is a newer version of libpurple.dll provided at http://pidgin.im/~nosnilmot/2.6.1/srvfix/libpurple.dll.
For portable version replace libpurple.dll in .\PidginPortable\App\Pidgin with one linked in bug report mentioned above.
E