Error in xy.coords(x, y, xlabel, ylabel, log) : x and y lengths differ

I am currently trying to use R to construct a regression model to
explain output based on temperature. I have combined my output and temp
data into a notepad file. there is no problem with loading the data into
R.

data.df

    output temp
1    850   17
2    849   17
3    905   17
4    925   17
5   1043   19
6   1104   20
7   1097   18
8    979   19
9    926   18
10  1133   18
~~
~~
240 1124   12
241 1344   12
242 1375   11
243 1359   12

but when I try to plot the data I keep getting this error:

plot(temp,output)

Error in xy.coords(x, y, xlabel, ylabel, log) : 
        x and y lengths differ

any advice on how to over come this error would be greatly appreciated.

Cheers, Robbie.