Intel Mac :: Why Do Network Preferences Keep Changing And Disconnecting WiFi After Sleep

I have an iMac OS X 10.7.3 (purchased in late 2010) with all updates current. I use AirPort to connect to my Linksys router with a WPA2 password.

Nearly everytime I wake my computer from sleep, my wireless router is disconnected, even when I have set my settings and clicked on the lock to prevent further changes. My router always shows on the list of available connections with full strength, but it is more often than not extremely difficult to get it connected again. It says "Could not join "myRouter". A connection time out occured."  I usually have to use the assistant and go through the steps, which usually includes re-typing my password four to five times before it agrees that I know my own password (which is fairly simple to type, I can't possibly be entering it incorrectly that many times).

I downloaded and installed an update [URL] that quote: "resolves an issue that may cause an iMac to not automatically connect to a known Wi-Fi network after waking from sleep. It is recommended for all iMac (Late 2009 or newer) users running 10.7.3."  

I tried setting a new location, and set the DHCP setting under TCP/IP to be manual. I was successful in connecting to the internet that time, and locked the settings to prevent further changes, yet the first time my computer woke from a sleep, the lock was unchecked and the settings were changed back to automatic. And I was disconnected yet again. 

This has been going on for months, but in the last couple weeks I have found I am now unable to lock the lock to prevent changes, no matter if my Location is set to automatic or one that I have created. Really looking for resolution as this is wasting so much time, I am on and off the computer multiple times a day. 

Info:
iMac, Mac OS X (10.4.11)