What happens if you run the installer as administrator?
Open an administrator command prompt and assuming that the calibre installer msi file is in your Downloads directory, at the command prompt enter:
Code:
msiexec /i "C:\Users\%username%\Downloads\calibre-64bit-6.28.1.msi"
A couple of other things to check are your antivirus settings and the security on the calibre2 directory to ensure that you have enough rights.