I installled latest version of gantry and the free gantry template for joomla 1.6.
I replicate a working menu that i had ready in joomla 1.5 in template maelstrom.
When i published 1 module position in the menu the default theme for gantry (free) joomla 1.6 crashes with the above error
Fatal error: Call to protected method JModuleHelper::_load() from context 'GantryFusionLayout' in /home/*******/public_html/dev/templates/rt_gantry_j16/html/mod_roknavmenu/themes/gantry-fusion/layout.php on line 286
if i use anothe template for 1.6 (tachyon) menu and module shows ok.
so i think there is a bug with default theme of gantry.