When installing v7.8 over v7.6, the installer stops with an error message: "Service 'Shavlik NetChk Console Service' (STConsoleSvc) could not be installed. Verify that you have sufficient privileges to install system services."
I executed the installer as an administrator, so I can't imagine what privileges I might not have.
Are there any corresponding Windows Event log entries which would provide more insight? You can also install NetChk Protect from a command line (using an administrator elevated command prompt) with some switches which will cause a log file to be generated (which, again, might provide more insight). The syntax is as follows (where '[installer]' = the name of the installation file which you are using: