so yeah the title sums it up, i download the 3.5.6f4 update of unity after downloading when i try to install unity normally i get the NSIS error and then i try the NSIS fix by placing the destination of the installer.exe of unity and adding /NCRC and it works however when i do this during installation the setup crashes so yeah both ways can’t get it work, i am using win 7 ultimate 64-bit, i don’t know what happened i never get this kind of problem before, and it is has become so hard to update and download new versions of unity.
try to re download it again~
i had the same problem… Then i uninstalled my anti virus (ESET Smart Security 5), redownloaded Unity, installed Unity, re-installed antivirus. And all work 