When I try to instal the beta version I get the message 'This operation cannot be completed because you do not have sufficient privileges for some of the items' Any idea what thats all about?

Make sure you have administrator privileges on your OS X account (if it is a machine at the office and not your home computer).

Also try to repair permissions using Disk Utility.

And just in case, try to re-download as there might have been a download issue.

I'm having the same problem with version 2.8.0.722. I tried all three of Dimitris' suggestions and also rebooted the computer for good measure. Each time, I got the same error message.

yup I'm having the same problem