'Subscript indices must either be real positive integers or logicals... and they are.' Why the error?

I keep getting the following error when I try to plot to vectors of data and it doesn't make sense to me. Does anyone know why this is happening?

x =

   1.0e+04 *

   3.592304700000000
   3.631143000000000
   3.684712000000000
   3.722212000000000
   3.767748400000000
   3.833372000000000
   3.886942000000000
   3.935166400000000
   4.007484799999999
   4.075794999999999

>> y

y =

   2.052695376905927
   2.116785788400099
   2.203573844584633
   2.266329782184324
   2.342437651581077
   2.450590377072377
   2.538714605463729
   2.628180700403267
   2.745678639284237
   2.865853118409325

>> isreal(x)

ans =

     1

>> isreal(y)

ans =

     1

>> plot(x,y)

Subscript indices must either be real positive integers or logicals.

[Brendan Hamm]

Likely, you have a variable named plot in the workspace, so MATLAB thinks you are trying to index into the variable and not call the plot function. Therefore the error is about an index and not a function input.

[Matt Brown]

Bingo! Thanks.