ERROR #6353: Unexpected attributes for element button (7,66): onselect

Somewhere in your button tag, you have onselect= something. Buttons don't have an onselect, but even if they did, I'm guessing that's not the event you actually want. onselect happens when a user highlights text within a control, like in a text input.

If you're trying to set what happens when the user clicks the button, that's onclick.

If you're trying to set what happens when the user selects the button but doesn't click it (say by pressing tab until the button is highlighted) that's onfocus.