So i sniffed around the code abit.
In Assets\XML\Units\CIV4MissionInfos.xml
<Button> refers to a non existing .dds
Same applies for MISSION_BOMBARD which uses the same button.
The .dds is named Barrage.dds in that folder but no mission afaik (not 10000% sure) uses it.
I copied and renamed the .dds to avoid having to check the entirety of the code so both barrage.dds and bombard.dds are there... both the same Art.
I ll see if it works once i can run Civ in a bit.
Edit: Ok checked it works now
Edit 3224: Found <Type>MISSION_ABOMBARD</Type> which is a <EntityEventType>ENTITY_EVENT_BOMBARD</EntityEventType> had barrage.dds for it's button. Might as well correct this mission's button and rename the entry in the art/interface/buttons/actions folder to "bombard.dds" .
In Assets\XML\Units\CIV4MissionInfos.xml
Spoiler :
<Type>MISSION_RANGE_ATTACK</Type>
<Description>TXT_KEY_MISSION_RANGE_ATTACK</Description>
<Help>TXT_KEY_MISSION_RANGE_ATTACK_HELP</Help>
<Waypoint>NONE</Waypoint>
<EntityEventType>ENTITY_EVENT_BOMBARD</EntityEventType>
<iTime>10</iTime>
<bTarget>0</bTarget>
<bBuild>0</bBuild>
<bSound>1</bSound>
<HotKey>KB_B</HotKey>
<bAltDown>0</bAltDown>
<bShiftDown>0</bShiftDown>
<bCtrlDown>0</bCtrlDown>
<iHotKeyPriority>0</iHotKeyPriority>
<HotKeyAlt />
<bAltDownAlt>0</bAltDownAlt>
<bShiftDownAlt>0</bShiftDownAlt>
<bCtrlDownAlt>0</bCtrlDownAlt>
<iHotKeyPriorityAlt>0</iHotKeyPriorityAlt>
<bVisible>1</bVisible>
<Button>,Art/Interface/Buttons/Actions/Bombard.dds,Art/Interface/Buttons/Actions_Builds_LeaderHeads_Specialists_Atlas.dds,2,1</Button>
<Description>TXT_KEY_MISSION_RANGE_ATTACK</Description>
<Help>TXT_KEY_MISSION_RANGE_ATTACK_HELP</Help>
<Waypoint>NONE</Waypoint>
<EntityEventType>ENTITY_EVENT_BOMBARD</EntityEventType>
<iTime>10</iTime>
<bTarget>0</bTarget>
<bBuild>0</bBuild>
<bSound>1</bSound>
<HotKey>KB_B</HotKey>
<bAltDown>0</bAltDown>
<bShiftDown>0</bShiftDown>
<bCtrlDown>0</bCtrlDown>
<iHotKeyPriority>0</iHotKeyPriority>
<HotKeyAlt />
<bAltDownAlt>0</bAltDownAlt>
<bShiftDownAlt>0</bShiftDownAlt>
<bCtrlDownAlt>0</bCtrlDownAlt>
<iHotKeyPriorityAlt>0</iHotKeyPriorityAlt>
<bVisible>1</bVisible>
<Button>,Art/Interface/Buttons/Actions/Bombard.dds,Art/Interface/Buttons/Actions_Builds_LeaderHeads_Specialists_Atlas.dds,2,1</Button>
<Button> refers to a non existing .dds
Same applies for MISSION_BOMBARD which uses the same button.
The .dds is named Barrage.dds in that folder but no mission afaik (not 10000% sure) uses it.
I copied and renamed the .dds to avoid having to check the entirety of the code so both barrage.dds and bombard.dds are there... both the same Art.
I ll see if it works once i can run Civ in a bit.
Edit: Ok checked it works now

Edit 3224: Found <Type>MISSION_ABOMBARD</Type> which is a <EntityEventType>ENTITY_EVENT_BOMBARD</EntityEventType> had barrage.dds for it's button. Might as well correct this mission's button and rename the entry in the art/interface/buttons/actions folder to "bombard.dds" .