Buildcraft version: 7.99.7
Forge version: 13.20.1.2429
Link to crashreport or log (on pastebin or gist, please don't put the entire log here) :
Singleplayer/multiplayer:

Additional information:
Hello i use galacticraft 4.0.0.117 and when i spill fuel and take in to bucket i has galacticraft fuel and i cant use it on engine can you solve it?

most likely galacticraft is also registering fuel and forge is using it as the dominant fuel yet it's not registered in the registry as fuel?

Closing for a lack of information, if you provide the requested information we can re-open and take another look at this.