GUI Tools for OpenConnect
Support for OpenConnect in NetworkManager has been integrated into GNOME git and is released alongside NetworkManager's other VPN modules: http://ftp.gnome.org/pub/GNOME/sources/NetworkManager-openconnect/.
Prior to OpenConnect v3.00, the auth-dialog tool which handles GUI authentication was part of OpenConnect itself, rather than included in the network-manager-openconnect package. Versions of network-manager-openconnect earlier than 0.8.4 will expect the auth-dialog to be provided for them, and thus will not work with a version of OpenConnect any newer then v2.26.
To use OpenConnect v3.00 or newer with NetworkManager, you will need to be using NetworkManager-openconnect v0.8.4 or newer.
Note for KDE users: KDE does not support using OpenConnect with version 0.8 of NetworkManager (unless of course you run OpenConnect manually from the command line and don't use NetworkManager for the VPN at all). It is only supported since 2011-06-22 with the NetworkManager 0.9, and with the corresponding nm09 branch of the kde-plasma-networkmanagement widget.
This support was added by Ilia Kats, as KDE bug #226028.