The covariance matrix being returned from Maxlik (or CMLMT) is a missing value and I am getting the error message "Hessian calculation failed". Why is this happening?
If the covariance matrix is a scalar missing value and the “Hessian Calculation failed” message is issued, the calculated Hessian has failed to invert. This means it contains linear dependencies. These dependencies can be due to poor scaling of the data, catastrophic failure of precision, or unidentified parameters in your model.