Smart Panel 3.x (Windows) > Error & messages > Why does the error message "Unknown error" appear when trying to install Smart Panel 3.6 upgrade program?
The problem may occur when there is a conflict during the installation.
 
In fact, this upgrade program allows you to install version 3.6 directly without previson versions (version 1.00 throught version 3.20) installed on the computer.
 
Please try to fully uninstall the previous version and then install Smart Panel 3.6 directly and see if the problem can be resolved.