covariance step

Dear NONMEM users: I have a data set for 30 infants where I am running a 2 COMPT PK model. I got the following error message for the covariance step. I need some help with trying to fix this error. Any suggestions? should I increase the upper boundries of initial estimates? MINIMIZATION SUCCESSFUL NO. OF FUNCTION EVALUATIONS USED: 289 NO. OF SIG. DIGITS IN FINAL EST.: 3.0 0PARAMETER ESTIMATE IS NEAR ITS BOUNDARY THIS MUST BE ADDRESSED BEFORE THE COVARIANCE STEP CAN BE IMPLEMENTED any help is appreciated. Thanks Varsha Mehta, MS(CRDSA), Pharm.D., FCCP Clinical Associate Professor Pharmacy, Pediatrics and Communicable Diseases Clinical Pharmacist Neonatal Critical Care University of Michigan (O) 734-936-8985 (F) 734-936-6946 [email protected] ********************************************************** Electronic Mail is not secure, may not be read every day, and should not be used for urgent or sensitive issues