I don't understand you completely. Do you mean:
1 You have RFCBritania loaded.
2 You try to load your scenario.
3 It tries to reload the mod and fails.
1 You have RFCBritania loaded.
2 You try to load a vanilla scenario.
3 It tries to reload the mod and fails.
If it is the upper one, it might be this. Open the the Scenario with a
text editor. You will see the following (this is from RFCE)
Code:
BeginGame
Tutorial=0
Era=ERA_ANCIENT
Speed=GAMESPEED_NORMAL
Calendar=CALENDAR_DEFAULT
Option=GAMEOPTION_AGGRESSIVE_AI
Option=GAMEOPTION_NO_TECH_BROKERING
Victory=VICTORY_TIME
Victory=VICTORY_DOMINATION
Victory=VICTORY_CULTURAL
Victory=VICTORY_DIPLOMATIC
Victory=VICTORY_HISTORICAL
GameTurn=0
MaxTurns=500
MaxCityElimination=0
NumAdvancedStartPoints=720
TargetScore=0
StartYear=500
Description=TXT_KEY_WB_DESC
[COLOR="Red"][B]ModPath=Mods\RFCEurope[/B][/COLOR]
EndGame
The problem might be that the last line (I made it red) is missing or has a different path. Make sure the path is correct. (So change RFCEurope in the name of your mod. (The name of the folder)
If it is the other thing, I'm not sure what the problem is. It could the the fact that your mod has many changes. So a normal scenario will conflict with it.