If you are using Mac OSX 10.6 (Snow Leopard) and are unable to install Sure Cuts A Lot or eCAL with the following error:
"The installation failed. An unknown installation error occurred. The Installer encountered an error that caused the installation to fail. Contact the software manufacturer for assistance."
You will need to update your Apple Software Installer from here.
http://support.apple.com/kb/DL1512