=COUNTIF(Sheet1!B1:U2,"1")/COUNT((Sheet1!B1:U2)*100)
Take the ( in red out, thats whats messing it up
it should be =COUNTIF(Sheet1!B1:U2,"1")/COUNT(Sheet1!B1:U2)*100
The whole result needs to be *100 not just the results of the count (second part)
for example your formula (with the brackets)...