Really slow to open drawings from explorer

[yrnomad]

I've got a user that just got a windows 7-64bit & autocad 2012 - 64bit.
When he opens drawing (even on his local drive) by selecting it through explorer rather than opening cad then browsing for the file, it takes significantly longer. I'd guess 4 times as long. It seems to hang for a bit, then finish loading.
Any suggestions, or is this a common glitch?

[SLW210]

Try disabling Digital Signature Valadation.

[ReMark]

Is AutoCAD already opened?

[yrnomad]

Sorry guys for disappearing.
First my user was "too busy" to work through the problem, then my time came to bug out of here for a week. woohoo!
So the status is, the delay has disappeared. I did some tinkering the week before when he was away from his desk. I turned off the Digital Signature Validation, but that had no improvement. I removed all our startup lisps even though that should have affected it whether loading Autocad first or loading autocad and dwg through explore and surprise... still no improvement.

So while I was gone, it stopped having the lag just as mysteriously as the lag came on a few weeks before. So, I guess that means it may come back again... but the user is happy for now.