sry to hear that. I can clearly attest to the instruction because I've successfully installed the unofficial mod numerous times, including the latest 4.2
Create a character immediately after the vanilla installation,
play single-play, load up the multi-play login screen after EACH legacy patches(1.2 and 2.0)
After that, the mod installation should go without a hiccup.
I have Microsoft .Net framework 4.5 installed.
also recommend to restart your computer upon getting the error message and re-try.
In my case, I almost always get an error message for the first time loading characters
after newly installing an unofficial mod. the problem goes away when I reboot.