Standard error for estimates

Hello everybody I am using Nonmem VI to model some Population Pk (10 subjects) data that I have. When I run this file.. I get the parameter estimates. However I fail to get any STANDARD ERROR of the estimates. I do sometimes get the R,S, T matrices when I change my initial estimates. Also the output file has following messages MINIMIZATION SUCCESSFUL MATRIX ALGORITHMICALLY SINGULAR AND ALGORITHMICALLY NON-POSITIVE-SEMIDEFINITE 0R MATRIX IS OUTPUT 0COVARIANCE STEP ABORTED My understanding (maybe I got it wrong) is that these R,S, T matrices are printed out when there are more than one solutions to the parameter estimates. is this right or does my control stream have some error within it. I checked the individual plots with the output data file. The individual and population predicted fits are quite decent.. It also gives me the following error message in the dos window (WARNING 50) OPTION "UNCONDITIONAL" OF $COVARIANCE RECORD IS IGNORED WITH THIS RELEASE OF NONMEM. Could someone kindly help me with what is the error in my control stream or how would I be able to get the Std error for the estimates $PROBLEM PK $INPUT ID TIME AMT MDV DV EVID CMT $DATA file1.csv IGNORE=C $SUBROUTINE ADVAN6 TRANS1 TOL=5 $MODEL COMP=(DEPOT,DEFDOSE); COMP=(CENTRAL);PLASMA $PK F1=THETA(1)*EXP(ETA(1)+ETA(2)) K12=4;Abso constant TVCL=THETA(2);Clearance CL=TVCL*EXP(ETA(3)) TVVC=THETA(3);vol of dist of drug VC=TVVC*EXP(ETA(4)) K20=0.20;elim rate const of drug VC=CL/K20 S2=VC; OUTPUT IN ng/ml $ERROR IPRED=F IRES=DV-IPRED DEL=0 IF (IPRED.EQ.0) DEL=1 IWRES=(1-DEL)*IRES/(IPRED+DEL) Y=F+F*ERR(1) $DES DADT(1)=-K12*A(1) DADT(2)=K12*A(1)-K20*A(2) $THETA (0.01,0.5,0.8); bioavailability (75 FIXED);CL (375 FIXED);VC $OMEGA $SIGMA $ESTIMATION METHOD=1 SIGDIGITS=2 MAXEVAL=9999 PRINT=5 POSTHOC $COVARIANCE UNCONDITIONAL $TABLE ID TIME AMT MDV DV EVID CMT IPRED IWRES IRES NOPRINT ONEHEADER FILE=sdtabsab335 thanks a lot