I'm getting the above error message and I cannot figure out why?

buildPair =

    do

arr <- newArray ((1,1),(1,10)) 37 :: ST s (STArray s (Int,Int) Int)

a <- readArray arr (1,1)

        writeArray arr (1,1) 64

        b <- readArray arr (1,1)

        return (a,b)

main = print $ runST buildPair