If you check the faq page (or bug one) there is a brief description of why that problem happens. Basically look for BerserkData in your main M&B folder. Rename it to Data. Rename the current Data folder to NativeData. You will have to rename them back to play other mods. The next release will have all the Data files in a data file within the mod folder and this problem won't exist. This will make use of ironlauncher.