Your network settings have been changed by another application FIX, PATCH, STOP, CORRECT

1. Open system preferences

2. Open "Sharing" under "Internet & Network"

3. Switch from the default "Services" menu to the "Internet" menu (you don't need to start sharing, or stop sharing, or check any boxes, or make any changes. Just switching menus is all you need to do)

4. NOW, WITHOUT CLOSING THE FILE SHARING WINDOW Click "Show All" at the top of the file sharing window

5. Open "Network" under "Internet & Network"

The pop up should be gone. It works for me and numerous other folks on OS 10.4

NOTE: You'll have to do this quick and easy fix (homemade "patch" if you prefer) each time you go to "Network" preferences, but you usually don't have go there often. Remember: DON'T CLOSE THE SHARING WINDOW - JUST CLICK DIRECTLY ON "SHOW ALL" AT THE TOP OF THE WINDOW, THEN OPEN NETWORK.