I have prepared a model to estimate genetic and environmental influences (ACE) using a cholesky decomposition with ordinal twin data: 3 phenotypes, 7 categories in each of them. The sample is is divided in 6 groups (and so is the script), according to zygosity and sex: MZ men, DZ men, MZ women, DZ women, DZ man-woman and DZ woman-man. The script including this multivariate threshold model takes about an one and a half hour to be computed, and returns the following error:
"NPSOL returned a non-zero status code 3. The nonlinear constraints and bonuds could not be satisfied. The problem may have no feasible solution."
Any help to interpret the meaning of this error message would be very much appreciated. Is there any possibility to solve it? I have attached the script with the model in case somebody need to have a look.
Thanks a lot in advance!