This worked in the upper part of my program with different parameters:
CL(k + 1) = (1 - Math.Cos(zL(k + 1) ^ 0.5)) / zL(k + 1)

previously worked as:
C(k + 1) = (1 - Math.Cos(z(k + 1) ^ 0.5)) / z(k + 1)

They were in a loop interrupted by an "if" and a "goto"


Run-time error "5":
Invalid procedure call or argument.