As of RailCraft 9.7.0.0, IC2 API is only partially provided which cause issues when another mod detects it.
If you really want to provide the API, please do provide it fully.
It would be even better to not include it at all and use CPW common lib and have optional interfaces and methods, like so:

@Optional.InterfaceList({
    @Optional.Interface(iface = "ic2.api.xxx.yyy", modid = "IC2")
    })
public class MyClass extends Item implements ic2.api.xxx.yyy {

and

    @Optional.Method(modid = "IC2")
    public void updateEntity() {