the temp folder is on a drive that is full or is inaccessible. free up space on the drive or verify that you have write permission on the temp folder.

This error message occurs when you are running Windows Vista (possibly 64bit), and have User Account Control turned off (first thing I did) and are trying to install Adobe Reader 8. To fix the error, put UAC on, or right click on the setup and go to properties -> Compatibility - Run in compatibility mode for XP SP2. It should work fine.