Which mod are you trying to install? It sounds as if you have not extracted the mod. You have to extract it and create a folder containing multiple files. Keka's default action with an unknown file is to compress it. It does not know that a .civ5mod file is a compressed (7z) archive unless you tell it so. There are a couple of ways to to this. The best method is described in the first post - download and install my modified copy of the Keka preferences. This adds .civ5mod to Keka as a known compressed file type, so when you drop one of these files onto it, it extracts it. If you are not happy with swapping preferences files, then I described an alternative method in post #263 earlier in this thread. Yet another option is to change the .civ5mod file name extension to .7z, which Keka does recognise.