[SOLVED] "Trying to call method on object of type: `Folder` with incorrect arguments."?

I am trying to code various player stat bars, and I made a function to calculate the percentage of stat health to max stat health, and then to apply it to the GUI bar size.

'playerstats' is a folder within Player that holds several stat IntValues. Here is my function:

function statChange(player, stat)
    for x in player.playerstats do
        if x.Name == stat then
            percent = x/maxstathealth -- percent is defined above as 'local percent', and 'local maxstathealth = 100'
        end
    end
    for x in screengui do -- I have various frames within screengui that are named after the stats
        if x.Name == stat then
            x.Size = UDim2.new(percent, 0, 1, 0)
        end
    end
end

I get the error "Trying to call method on object of type: Folder with incorrect arguments." on the second line:

for x in player.playerstats do

I'm not entirely sure what this means, or how to fix it. Thank you very much in advance!