SimBiology

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I am using SimBiology Model Analyzer to fit a model from my data using nonlinear mixed-effects estimation. I select the 'Fit Data' program after loading the data from the Excel file. I select the model as 'mPBPK_base' and setup the data and response accordingly. I try to run the fit using 'mixed effects' statistical modeling. The transformation is exp(theta1+eta1). The 'error model' is 'constant'. Under 'Algorithm settings', 'ApproximationType' is set to 'FOCE'. This produces the following error:   error After the initial refinement of the fixed effects with the Levenberg-Marquardt algorithm some columns of the Jacobian are effectively zero at BETA0, indicating that the model is insensitive to some of its parameters. That may be because those parameters are not present in the model, or otherwise do not affect the predicted values. It may also be due to numerical underflow in the model function, which can sometimes be avoided by choosing better initial parameter values, or by rescaling or recentering. I then changed the ‘RefineBeta0’ to ‘off’ in the Advanced Algorithm Settings, which was supposed to be more robust in fitting. But I get the following error:   error A simulation errored or returned NaN, Inf, or complex values during parameter estimation. This typically indicates that the estimated parameter values converged to values that are invalid for the model. Why do I get these errors? Is there any robust way to fit my model? kA03q000000t1rcCAA 000335620