Error msg. Subscript out of range

I am trying to get my head around some VBA and ran across a video series on you tube that seems to be easy enough for an old novice to grasp, however in a very early lesson I am trying to complete this example but I am running into a wall.

When I try to run the following code I get an Error message "Subscript out of range" and I have been unable to get any further. I have tried renaming the target sheet but to no avail. I am at an impass. Any ideas?

The series is done by Excel VBA is Fun. This is the link to the lesson.

HTML Code: 

Sub StartTimer1()
    nr = ThisWorkbook.Sheets("Timer").Cells(Rows.Count, 1).End(x1up).Row + 1
    Cells(nr, 1) = Time
End Sub

Thanks
Jim O