Two thoughts:
1. One or more of the textures in the \texture folder is missing
2. Check you have this entry in the panel.cfg file:
[Vcockpit01]
size_mm=1024,1024
visible=0
pixel_size=1024,1024
texture=$<the_aircraft_name>
I did forget to mention that the VC worked flawlessly in P3Dv4.5 but stopped working correctly in P3Dv5. The entire aircraft/A380-800 folder was copied and pasted from one sim to the next. All the original VC textures are in the texture.vc folder, but it seems that texture folder resides outside of the panel folder, but rather in the main airplane folder SimObjects/Airplanes/A380-800/texture.vc ... to be honest, looking through this aircraft folder, it seems like it is a bit of a mess. 1) The texture.vc folder (which has virtual cockpit textures) is made as if a texture folder for a livery and placed into the main folder, 2) Inside the panel folder is another folder called tom340 which has more textures in it (just over 100 textures mostly buttons/switches), 3) The panel.cfg is calling for textures that reside directly within the panel folder and not within the panel folder and not organized at all, 4) [Vcockpit01] lists the texture as being $A321_1 but that texture does not exist in the panel folder nor in any of the sub folders but instead has $A321_2 in the panel folder ... There is a texture called A321_1_L.dds (along with ..._T , ..._T_Bump , ..._T_LM , and ..._T_spec) within the texture.vc folder, but I do not see that folder called anywhere in the entries below.
Panel.cfg has these entries for the VC:
[Vcockpit01]
Background_color=0,0,0
size_mm=1024,1024
visible=1
pixel_size=1024,1024
texture=$A321_1
gauge00=Airbus_A321!annunciator_panel_1, 680,832,339,79
gauge01=Airbus_A321!autopilot, 685,914,339,110
gauge02=Airbus_A321!pfd_mfd_select_panel, 477,914,207,110
//gauge03=Airbus_A321!ecams, 3,302,283,282
gauge03=tom340!ecams, 3,302,283,282
gauge04=Airbus_A321!ecams2, 301,298,283,282
gauge05=Airbus_A321!mfd, 299,3,285,285
gauge06=Airbus_A321!pfd, 4,4,283,282
gauge07=n_number_plaque!n_number_plaque, 627,888,48,13
gauge08=Airbus_A321!altimeter_backup, 793,2,93,95
gauge09=Airbus_A321!attitude_backup, 893,8,125,125
gauge10=Airbus_A321!hsi_backup, 886,131,134,159
gauge11=Airbus_A321!ias_backup, 677,661,91,94
gauge12=Airbus_A321!popup_clock, 758,198,122,122
gauge13=Airbus_A321!popup_gear, 594,0,165,182
gauge14=Airbus_A321!popup_ecams_screen_bezel, 592, 186 ,136,140
gauge15=Airbus_A321!popup_radio, 781,532,236,284
gauge16=Airbus_A321!popup_glass_panel_small, 592,184,134,141
gauge17=tom340!popup_overhead, 3,588,583,262
gauge18=tom340!popup_ecu, 591,350,183,289
gauge19=CALLOUT_SOUND!dsd_xml_sound3, 0,0,0,0, Sound\CALLOUTB\Sound.ini
gauge20=CALLOUT_SmallJets!CALLOUT2500, 0,0,0,0
gauge21=CALLOUT_SmallJets!CALLOUT1000, 0,0,0,0
gauge22=CALLOUT_SmallJets!CALLOUT500, 0,0,0,0
gauge23=CALLOUT_SmallJets!CALLOUT100, 0,0,0,0
gauge24=CALLOUT_SmallJets!CALLOUT50, 0,0,0,0
gauge25=CALLOUT_SmallJets!CALLOUT40, 0,0,0,0
gauge26=CALLOUT_SmallJets!CALLOUT30, 0,0,0,0
gauge27=CALLOUT_SmallJets!CALLOUT20, 0,0,0,0
gauge28=CALLOUT_SmallJets!CALLOUT10, 0,0,0,0
gauge29=CALLOUT_SmallJets!CALLOUTMIN, 0,0,0,0
gauge30=CALLOUT_SmallJets!CALLOUTAPPMIN, 0,0,0,0
//--------------------------------------------------------
[Vcockpit02]
file=$A321_2.bmp
Background_color=0,0,0
size_mm=512,512
visible=1
pixel_size=512,512
texture=$A321_2
gauge00=SimIcons!GPS Icon, 275,97,26,18
gauge01=SimIcons!Map Icon, 470,97,27,17
gauge02=SimIcons!ATC Icon, 275,118,26,17
gauge03=SimIcons!Kneeboard Icon, 470,119,26,16
gauge04=HoneywellFMC!fmc, 0,0,256,417
This thing needs some spring cleaning, but I am not quite sure where to place things so that links aren't broken and no more space than necessary is taken up (copy contents of every folder and place them in all folders in case the map is just wrong). All the buttons and switches that are supposed to work work, and the guages work, it is just the panel textures and backlight are not working.