Please help, I get this error. It is the exact same error that the new forestry and IC2 created before Forestry updated its IC2 api. The error occurs when you mod and the other two are installed. Please update your API so the mods can work together again
Try to delete the IC2 folder in the MFFS zip file. Usually this kind of problem occurs if the API of another mod changes. The older version of that API is still available through one of the other mods, like MFFS in this case.
It's always a good idea to delete the bundled API's in mods if you have the referenced mod installed, so remove IC2 API folder from all mods except from IC2 itself.