Please try the following:

Check the My_Computer_Zone has FullTrust permissions enabled:

1. Click Start
2. Click Control Panel
3. Double-click Administrative Tools
4. Click to select the latest version of the Microsoft .NET Framework
Configuration tool.
5. Drill-down to Runtime Security Policy
6. Then Machine
7. Then Code Groups
8. Then Machine
9. Code Groups
10. All_Code
11. Then Right-click on My_Computer_Zone.
12. Click the Permission Set tab
13. Verify and/or change permission set to FullTrust.
14. Reboot the machine
15. Try the installation once more and see if this works for you.

 

 

 

All of my searches for this error return old 2006 posts about it. (Pre release Vista RC1,2)

 

http://www.eggheadcafe.com/software/aspnet/30257265/0x643-installing-framewor.aspx

 

http://forums.microsoft.com/MSDN/ShowPost.aspx?PostID=1845440&SiteID=1

Mine is already set to full trust and the update will still not install (get the error code 643). 

 

I've also tried several suggestions on the Microsoft site and get the same thing. 

also, check your date, time and time zone. :-)

My date/time is set correctly.

 

With the number of people having the problem it has to be something in the update.

Bill, I've downloaded the update separately from MS and it still will not install. 

Along with everything else I've seen on the Error 643 on the Microsoft site, here on the forum and elsewhere, nothing fixes it for me.  I tried uninstalling Net Framework 1.1 and the OS will not let me uninstall it.   I tried downloading and installing Net Framework V3 and that will not install.  My user profile is full Administrator Priviledges.

 

I've just "hid" the update for the time being and hopefully MS will issue a corrected update that addresses the problems.