Network Not Selected Message

When I wake my computer I get a box that says "none of your networks is selected" In the box are a bunch of networks some with locks others without. When I got a new modem, we set up the netwok name. That name is in the box and has a lock next to it.

The strange thing is that the computer works properly as does the Kindle Fire which is in the other room so the router is working. Doesn't this mean the that my networks are selected and working but the message says no? Also, there does not seem to be an option for me to select so I don't have to see that message box every time.

Can someone suggest why I see that message?

Which Mac do you have and what version of OS X are you using? What you're reporting was a problem with Lion and certain MBP and iMac models. They would lose the network when waking from sleep. Apple has since fixed that problem with an update to Lion. Mountain Lion is OK.

I have the desktop Mac running os x 10.5.8. The correct wording of the message is "none of your preferred networks are available." To clarify - I get the message but don't actually lose the network.
Thanks

This happened to me when I changed my existing network from unprotected to protected. To fix it, try going to System Preferences, selecting Network, go to Advanced, select the WiFi tab, select the network, and delete it with the minus button. Then restart your computer.