This document explains two installation errors when trying to install Symantec Endpoint Protection 11. The solution to both of these issues is to manually uninstall Symantec.
If you receive the error "Symantec EndPoint Protection has detected that there are pending system changes that require a reboot", first try to reboot the computer. If the error persists, follow the instructions on this page: Manually Uninstalling Symantec Products
Another installation error involves an issue with the installation progress bar. If the progress bar rolls back twice, then closes without installing SEP, see this page: Manually Uninstalling Symantec Products