Re: Twinview fails + missing 'wfb' module
Solved, for now: inserting
Option "ModeValidation" "NoDFPNativeResolutionCheck"
allowed me to achieve 1600x1200 on the primary display.
To assist the marvellous nVidia chaps, I attach the last verbose log file prior to fixing the problem - it clearly indicates some kind of issue working out maximum acceptable resolutions.
Thanks to all and sundry.