Did you already request and obtain access to the ncas_generic group workspace, as suggested in the JULES FLUXNET tutorial?
contains the ancillary data for the vegetation on the WFDEI grid (0.5 degree LAT/LON spacing). As shown in the u-as052 suite, the variables used for the prescribed data sets for JULES are canht (canopy height) and lai (leaf_area_index).
For the GSW3-temp driving data file that you are trying to use, does that have a 10800-second data_period (3 hours)? Does it have the variable names listed in the jules_drive section of the file ~/roses/u-as052/app/jules/rose-app.conf ?