I'm testing a multilevel model with random slopes and a covariance structure for the error and reml terms, but I've been getting the following feedback:


. xtmixed btda yearA avgroa avgtam avgliq avgend i.setor avgpib avghdi avgpad_cpi avgpad_cpixyear if ifrs == 2|| sl: yearA, covariance(unstructured) || countrycod: yearA, covariance(unstructured) || id: yearA, covariance(unstructured) reml

Performing EM optimization:

Performing gradient-based optimization:

Iteration 0: log restricted-likelihood = 15332.862
Iteration 1: log restricted-likelihood = 15582.751 (not concave)
Iteration 2: log restricted-likelihood = 15593.999
Iteration 3: log restricted-likelihood = 15594.678
Iteration 4: log restricted-likelihood = 15597.363
Hessian is not negative semidefinite
conformability error
r(503);


Help me, please!!