Despite my best efforts, I couldn't figure out how to make a button default until I came across a helpful tip from someone here who shared some javascript code that checks for the enter key in a textbox and triggers the button.
I attempted placing my controls inside a form and setting the default button, but nothing seemed to work except for that javascript solution.
Now, the issue I'm facing is with an ajax extender that autocompletes the textbox by showing a dropdown list of values as you type. Users typically type part of something, navigate through the list using the down arrow key, and press enter to select an item.
However, pressing enter doesn't select the item due to the javascript code I implemented to trigger the default button. I'm not sure how to resolve this dilemma.
Interestingly, on one of my pages, the search button magically became the default button without any action on my part, so that page functions properly. On the other page, the button isn't set as default, and I can't seem to determine why!