When I first got my 4500, it ran great with no problems.
But after a few weeks, I started noticing problems such as you and others descibe with the wireless.
If you check the router logs, you will find that the problem isn't anything to do with the connection timing out.
From what I've seen, the router logs show
Client De-Authentication, plus there was one other message which I fail to remember. But the gist of the matter from the logs I've seen, seems to to indicate that the internal Wireless Client in the 4500 appears to having problems communicating with the router itself.
In other words, the router and the wireless client appear to be seperate components instead of being integrated together.
Either that, or there is a problem in the firmware which is causing it to appear this way.
I probably should have posted when I first noticed those errors in my router logs as I would at least have been able to provide the exact messages to explain why I said what I did in regards to the router - Currently, I have the Wireless completely disabled until such time as D-Link is able to provide a stable firmware with out this problem.
In the meantime, I'm running a wired GigaBit network in my home which in all actuality is a hell of a lot faster than the 300MB's I was getting with the wireless.
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I've got the DWA-643 Express card for my laptop and that works just fine when the connection works. But for now, it's put away until such time as I turn the wireless back on. For now, I just use an EC1000 GigaBit Express Card with my laptop seeing as D-Link doesn't sell any GigaBit Express Cards.