Re: Disable a button after it is pressed once
First - regarding the visibility of the button. If you want the button to not show, put the code in the Visible property. All you need is the variable, not any test if your variable is Boolean. If you are using Set(IsVoted,true) then you can just put !IsVoted in the Visible property and the button will not be visible once it is pressed.
The Disabled property will show the button, but will not allow it to function, and it will use a separate set of colors. This is often preferable, but in your case the Visible is fine.
The code I presented earlier to test for the presence of voting in the list should keep the data from being written if there is already a vote in the list. It would not disable the button - that would be up to the code above. If it is recording the data then there is an error in the code and it is not evaluating correctly.