I think that you just entered wrong texture names, I did the same mistake first time. For instance, full name of used texture file is "Robe_RaidMage_E_01Orange_Sleeve_AU_U.BLP", however, you have to enter only "Robe_RaidMage_E_01Orange_Sleeve_AU" into ItemDisplayInfo.dbc.
".BLP" part doesnť have to do anything there, thats obvious, but that "_U" (might by also "_F" or "_M") also has to NOT be placed into DBC. These endings of file names mean if texture should be used only for male, only for female or for both characters. If you place them into DBC, client isn't actually looking for "Robe_RaidMage_E_01Orange_Sleeve_AU_U.BLP", but for "Robe_RaidMage_E_01Orange_Sleeve_AU_U_U.BLP" (or "..._U_F.BLP"/"..._U_M.BLP"), which doesn't exist. You can encounter somehting similiar in model columns while making custom displayIDs for head items. They have different models for each combination of race and sex, but you enter only pure name of model, no "_orm" or "_hum" endings into DBC.