You have to run the file from terminal. open terminal by Ctrl + T. Enter sudo ./Downloads/SecondLife/secondlife .Change the names accordingly for the path.. (For this command the main file 'secondlife' is in SecondLife folder in the Downloads folder). You can shorten your original folder names for ease.
I use nvidia optimus drivers. If u have those, you will need to download bumblebee packages and use optirun command