"Zero field" message while trying to plot a vector field (continued)

Dear all,

I' m currently facing a problem while trying to make a plot with the version 6.0.0 of NCL. I've attached the script I'm running and the plot I get to this mail.

I'm trying to plot together 2 contour fields and a vector field on a vertical cross-section, using the functions "overlay", gsn_csm_contour and gsn_csm_vector. My data are 2D and have 2-dimensional vertical and longitudinal coordinates (height_1 and lon_1). I am also using the grid type "TriangularMesh" to make the topography appear at the bottom.
My problem is that I get a ZERO FIELD error message in the middle of my plot instead of the vectors, even if I could plot the 2 contour fields. Here is part of my script:

;;;;;;;
; Plot of the transects
wks = gsn_open_wks("x11","trans_lon_ctl_DJF")
gsn_define_colormap(wks,"hotcold_18lev")

;; 1st transect
r = True
r@trGridType = "TriangularMesh" ; To plot the topography
r@gsnMaximize = True
r@gsnDraw = False
r@gsnFrame = False
r@cnLinesOn = False ; no contour lines
r@cnFillOn = True
r@cnLevelSelectionMode = "ExplicitLevels"
r@cnLevels = (/-5,-2.5,0,2,4,6,8,10,12,14,16,18,20,22,24,26,28,30/)
r@gsnSpreadColors = True
r@sfXArray = lon_1
r@sfYArray = height_1
r@trYMaxF = 6000
cn_1 = gsn_csm_contour(wks,T_ctl_1(0,:,:),r)

r2 = True
r2@trGridType = "TriangularMesh" ; To plot the topography
r2@gsnMaximize = True
r2@gsnDraw = False
r2@gsnFrame = False
r2@cnLevelSelectionMode = "ExplicitLevels"
r2@cnLevels = (/0.05,0.1,0.15,0.2,0.25,0.3/)
r2@cnLineColor = "black"
r2@cnLineLabelPerimOn = False
r2@sfXArray = lon_1
r2@sfYArray = height_1
cn_2 = gsn_csm_contour(wks,QC_ctl_1(0,:,:),r2)

r3 = True
r3@trGridType = "TriangularMesh" ; To plot the topography
r3@gsnMaximize = True
r3@gsnDraw = False
r3@gsnFrame = False
r3@vfUDataArray = U_ctl_1(0,:,:)
r3@vfVDataArray = W_ctl_1(0,:,:)
r3@vfXArray = lon_1
r3@vfYArray = height_1
cn_3 = gsn_csm_vector(wks,U_ctl_1(0,:,:),W_ctl_1(0,:,:),r3)

overlay(cn_1,cn_2)
overlay(cn_1,cn_3)
draw(cn_1)
frame(wks)

I haven't found any information on how to manage this error in such a case, so any help would be really appreciated.
Regards,

Quentin

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