Rendering asteroid orientation as seen from Earth
From the paper by M. Kaasalainen, J. Torppa, and K. Muinonen, equation (1) is:
$$ \vec r_{ast} = R_z(\omega(t-t_0)+\phi_0) R_y(\hat\beta) R_z(\lambda) \vec r_{ecl} $$
To reverse this equation you must reverse the order of the rotations and the rotation angles:
$$ \vec r_{ecl} = R_z(-\lambda)R_y(-\hat\beta)R_z(-\omega(t-t_0)-\phi_0) \vec r_{ast} $$
From your description, you reversed the order of the rotations but not the rotation angles.