A curve, or not a curve, that is the question?

Of  course is what you define a parameter representation of an ellipse but "t" must run up to approx. 2.00641 s with an appropriate step size to make it really a "closed" one.

But how can you expect this curve having a LENGTH? You are operating in a plane where the horizontal direction is of dimension time^-1 while the vertical direction is dimensionless. How wold you define LENGTH or DIRECTION in this context?

To make it work you either have to make all dimensionless or make equal dimensions in any direction (preferably dimension length, otherwise talking about the "length" of the curve would not make much sense 😉
To make the point more clear: In the following plot we can say that the slope is  0,75 kV/ms, but what would you say is the "length" of that straight line segment? Which unit would you apply???

It seems to make no sense to ask for a "length" in this setting with units.

P.S.: You did not attach the worksheet and I am too lazy to retype - whats the error message. My translation tells me that it means something like "Are you a total fool?" but this would not be very polite for an official error message.