Hello everyone, I am fitting a multilevel (5 levels , 3 random intercept) of longitudinal data ( binary outcome) using proc glimmix. When I test a random slope ( age) on the lowest level. I got the following message: ‘Estimated G matrix is not positive definite ‘ and the covariance parameter estimate of slope is zero. It does mean that I don’t need the random slope age? ( that’s one of the suggestions for Proc mixed, not sure if the same applies to Proc glimmix). Any help  would be appreciated , Alda Code: proc glimmix data=PENPIG10   method=RSPL noclprint=20 ;; class   Age FarmID CohortID_C PenID_C PigID Nursc Envc Nursc4 Rxpc Subjpc Mortpc HthP Gender Season PenCat visit Tlw1wk_rtb; model PigSalmCult (event='Pos')= Tlw1wk_rtb Nursc4  Mortpc                                   Age FarmID    /solution link=logit dist=binary oddsratio ddfm=Kr; ; nloptions tech=nrridg;; random intercept/subject= CohortID_C; random intercept/subject=PenID_C (CohortID_C); random intercept Age /subject= PigID (PenID_C CohortID_C)type=VC; covtest/wald; Title' MT5.11.-Tlw72h_rtb Trend '; format  Nursc Envc HthP Tlw1wk_rtb YN. Nursc4 Rxpc Subjpc Mortpc  YNM.  Gender gender. PigSalmCult Cult. Season Season. PenCat PenCat. FarmID FarmID. TNZ12h TNZ.; run; ... View more