Hello, I tried to create a little Modpack for me and my freinds. But when I start Minecraft, I get the Error

Forge Mod Loader has found a problem with your minecraft installation
You have mod sources that are duplicate within your system
Mod Id : File name
....

did you by chanse add both the all in one jar (just labeled buildcraft-x.x.x) and all the module jars (buildcraft-module-x.x.x)? if so remove the modules, the all in one jar contains all the modules already

Perhaps, right here, it could be clearly stated something like: "The all-in-one jar is recommended over the modular jars. In addition, the core module includes the lib module. Installing both modules together will be loaded as a duplicate."

It could also be that this person downloaded compat, but that is clearly stated that it's in the all-in-one now.