Hi all I was trying to mosaic the MODIS aerosol MOD04 files to a big one. and the error appears as given in the title. could any help to debug this? thanks a lot. fids = LONARR(N_elements(index_yy_dd)) pos = LONARR(3, N_elements(index_yy_dd)) DIMS = LONARR(5, N_elements(index_yy_dd)) MAP_INFO =replicate(map, N_elements(index_yy_dd)) for i = 0, N_elements(index_yy_dd)-1 do begin envi_open_file, filelist[index_yy_dd[i]], r_fid= in_fid MAP_INFO[i] = ENVI_GET_MAP_INFO(fid = in_fid) envi_file_query, in_fid, ns=in_ns, nl=in_nl fids[i] = in_fid pos[*,i] = [0,1,2] DIMS[*,i] = [-1,0, in_ns-1,0, in_nl-1] endfor out_name = 'E:\Tibetan_NDVI_TP\MOD04L2\IN_IDL\not_stacked_mosaic\AOD_Land_correc_depth_' $ + strtrim(year, 1) + "_" + strtrim(day, 1) out_ps = [1000.0, 1000.0] georef_mosaic_setup, fids=fids, out_ps=out_ps, xsize=xsize, ysize=ysize,$ x0=x0, y0=y0, dims=dims ;, map_info=map_info use_see_through = [[1L], [1]] see_through_val = [[0L], [0]] envi_doit, 'mosaic_doit', fid=fids, pos=pos, dims=dims, out_name=out_name, $ xsize=xsize, ysize=ysize, x0=x0, y0=y0, georef=1, map_info=map_info, $ out_dt=4, pixel_size=out_ps, background=-1, see_through_val=see_through_val, $ use_see_through=use_see_through