My WebGUI hostsallow contained ONLY external IP addresses and not my local lan addres.

Solved it by editing (blanking) _hostsallowed variable in /etc/rc.d/lighttpd and restarting lighttppd.

PS: The script /etc/rc.d/lighttpd generates the config /var/etc/lighttpd; editing this config file directly does not work.

///

Temporary fix to regain access to WebGUI