Slider Expression Error

Yes turns out I was stupid all along, I put the expression in the slider effect rather than the source text area. That was the cause of the issue the entire time. When I looked closely, it even showed that on youtube. Thank you guys so much for trying to help. 

Where are you applying the expression? You'll probably get that error if you apply the expression to anything other than the Source Text property of a text layer.

It still shows an error for the first line of the expression saying "couldn't turn result into numeric value"

Forgot to mention that there are missing semicolons after your slider, sec, and min variables, so make sure to add those at the end of these lines

Try this on the Javascript expression engine:

slider = Math.round(effect("Slider Control")("Slider"))

sec = slider%60
min = Math.floor(slider/60)

function addZero(n) { 
	if (n<10) {
		return "0" + n;
	} else { 
		return n;
	}
}

addZero(min) + ":" + addZero(sec);