I was having this error too. The good news is I was able to fix it fairly easily. Here's how I did it:
1: Find the directory in windows explorer (C:\Program Data)
2: Right click on the 34BE82C4-E596-4e99-A191-52C6199EB69 directory and select properties.
3: Select the 'Security' tab.
4: In the 'Group or user names' box, there should be the following entries;
SYSTEM
Administrators (xxxx\Administrators)
Users (xxxx\Users)
(where xxxx is the name of your computer)
If these user names do not exist, create them by clicking on 'Edit' and then 'Add' and typing in the user name.
5: Set the permissions for these user names (using the 'Edit' button) as follows;
SYSTEM - check all boxes except 'Special Permissions'
Administrators (xxxx\Administrators) - check all boxes except 'Special Permissions'
Users (xxxx\Users) - check Read & execute, List folder contents and Read.
6: Rember to click 'Apply' after setting up each user name, and when you are done, just OK your way back out of the properties dialog box.
7. Now try to update itunes.
This fix worked for me 😉
I'm running windows 7, btw.
Hope this helps.