AV scan won't start

I have a Core 2 quad processor, Vista home premium 64bit & 8gb ram. When I try to run a Virus Scan, if it runs, it gets to “14 items scanned” then locks up. But usually it won’t start. At either case it gives an error message with this code “0x800705aa” (see attachment). I’m at a loss as to the problem. Any help? Thanks

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