Ok, the problem is that if you have in your custom assests dir a file which refers to another file that isn't there (because you have deleted it) or that is not made as it was supposed to be (because you have overwritten it with another one), you'll get an error or some strange effects, like blank pages etc. So, if you already have at least one mod and you want to install another one, you'll have to pay attention: if some of the files of the new mod have the same name and location of some of the file of the old one, you can't simply overwrite the old ones with the new ones, but you have to merge them (I've posted in various threads my merged files for the most common "unaltered gameplay mods"). Of course if the 2 files are identical, you don't have to merge anything. On the other hand, if you want to replace a mod with a new version, or with a different version made by some other guy, before installing the new one you'll have to delete all the files of the old version, but the ones that are in common with other mods. "In common" means that two mods use the SAME files, not a merged one. If the old version needed a merged file, you'll probably have to overwrite it with the original file from the other mod and leave it there or merge it with the new file, depending on the circumstances (if the new version has or has not a file with that name, and if that file is the same or is different from the file of the old version). If you don't do in this manner, you'll be lucky and have no probglem (if the two mods have no file with the same name or if they have in common the same file), but you have a big chance of getting a loading error, or some strange effect, or to loose some function of the mod. I was in the same situation when I changed from MSDA to CDA. You simply have to delete all the MSDA files which aren't in common with another mod, check if there is some MSDA files that you have previously merged with some other mod (in this case you have to replace them with the original files from the other mod) and finally install the CDA file. It worked fine for me.