NONMEM message

Dear all, I have a following error(?) massage on a poplation analysis using NONMEM VI. 0MINIMIZATION SUCCESSFUL HOWEVER, PROBLEMS OCCURRED WITH THE MINIMIZATION. REGARD THE RESULTS OF THE ESTIMATION STEP CAREFULLY, AND ACCEPT THEM ONLY AFTER CHECKING THAT THE COVARIANCE STEP PRODUCES REASONABLE OUTPUT. I found it when I described a control stream to assess sex difference on oral clearance as shown in below, TVCL = THETA(1) * THETA(2) ** SEX where SEX=0 for male and SEX=1 for female. This message was displayed without any error message. It was not dissapeared even though I changed the initial parameters. However, it was solved when I changed the model definition. For example, TVCL = THETA(1) IF (SEX.EQ.1) TVCL = THETA(2) Could you please let me know some details regarding the message. Especially, I'd like to know 1. What impact does this error message give the analysis result? 2. Why does it depend on the model definition? Thanks, _/ _/ _/ Mitsuo Higashimori, Ph.D. _/ _/ _/ Pharmacokinetic Group, Early Phase Development Department _/ _/ _/ Clinical Division, Research & Development _/ _/ _/ AstraZeneca K.K. _/ _/ _/ E-mail: [EMAIL PROTECTED]