Step 1: Check background programs.
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Disable firewalls or other Internet browser programs that can affect the Internet connection. The following programs can affect the connection to the Windows Update site and I suggest you remove or disable them:
McAfee firewall
Norton Internet Security
Zone Alarm Firewall
Panda firewall
Step 2: Delete the CatRoot2 folder
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A: Stop Cryptographic Services:
1. Click Start, click Run, type in "SERVICES.MSC" and press Enter.
2. Double click Cryptographic Services, and then click Stop (if it has been started).
B: After stopping Cryptographic Service, please delete the "Catroot2" folder:
1. Locate the "C:\Windows\System32\" folder.
2. Delete the Catroot2 subfolder in System32.
Note: I am assuming your Windows Vista is installed in C:\Windows.
C: Re-start Cryptographic Services:
1. Click Start, click Run, type in "SERVICES.MSC" and press Enter.
2. Double click Cryptographic Services, and then click Start.