Could not join "wifi network name". A connection timeout occurred.

Mac Pro running 10.7.5.

Whenever the computes wakes from sleep or logs in, it no longer automatically connects to my wifi network. When I manually select the network for from the Wi-Fi status in the menu bar, I get the following message: Could not join "wifi network name". A connection timeout occurred.

Even though I get that message the machine joins the network with no other problems. I am led to believe that is is on the Mac Pro as my Macbook and iPad/iPhone join the network with no issues.

I have tried deleting and restoring the preferred network, and remember networks is checked. I have also restored my airport express base station.

Any suggestions?