Law curve: Invalid Spine or law function data

Hi everyone,

I am trying to insert a law curve in NX 9 which defines an ellipsis which begins at CS origin and ends at a specific point P (x_p, y_p) at an specific angle. Lamda is the angle the ellipsis is supposed to have at point P. I am using the following expressions:

x = a*cos(-right_angle+right_angle*t+t*asine((y_p-b)/b))

and

y = b*sin(-right_angle+right_angle*t+t*asine((y_p-b)/b))+b

with:

a = abs(SQRT(x_p/(x_p*m^2-2*y_p*m))*(y_p-x_p*m)) [semi axis in horizontal direction]

b = y_p/(1-m*x_p/abs(m*x_p)*sqrt(1-(x_p/a)^2)) [semi axis in vertical direction]

m = tan (lamda)            [slope at point P]

t = parameter for law curve which goes from 0 to 1

lamda, x_p and y_p are constants which can be chosen freely. When I try to insert the law curve I get the error message "Invalid Spine or law function data".

I already copied the formulae into an excel sheet and the graph looks fine. So the equations should be correct. Any idea why this is not working?

CC-

EDIT: x_p must be > 0 for the equations of x and y

EDIT 2: the expression right_angle is defined as 90 degrees