MJS_JR

I bought the making history expansion pack yesterday however the installer says that it can't install it because i don't have KSP version 1.4.1 even though i do. I have re-downloaded the installer, installed the 1.4.1 version and its still telling me the software isn't the correct version even though it is, My computer meets the system requirements, as i've been playing it for ages without any issues. Can anyone help me with this.