From an incorrect date and time setting, firewalls to malware damage. Since it's error message 646 did you research that on google?
Bob
I am still having a problem downloaded my updates (critical) from Microsoft. Every time I try to download the updates, I get a message that says, "Error message 646 unable to download updates." Initially, I had 6 critical updates but now I have 17, can anyone help me with this issue?

Chowhound
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