Once again, Prime's notorious auto-labelling feature struck!
The "t" on the horizontal axis is labelled "automatic" but the "t" in your function call on the vertical axis is labelled "Variable".
If you label them identical, the plot works. I simply deleted the t in your function call on the vertical axis and retyped it again and this did the job as well.
Nevertheless defining a range for t as Valery had shown gives you a bit more control over the plot and you may prefer this approach.
