BAYES Estimation: OBJECTIVE FUNCTION IS INFINITE

Dear All, I am using a cascade of the EM estimation methods implemented in Nonmem 7.2 to solve a high-dimension PK/PD problem. The estimation chain is coded as below: $EST MET=SAEM INTER NBURN=2000 NITER=1000 PRINT=5 NOABORT NOPRIOR=0 ISAMPLE=10 SIGL=6 CTYPE=3 IACCEPT=0.4 CONSTRAIN=1 SEED=145612 FILE=Saem.ext $EST MET=IMP INTER NITER=2000 ISAMPLE=1000 PRINT=5 SEED=581987 SIGL=6, CTYPE=3 MAPITER=0 FILE=Imp.ext $EST MET=BAYES INTER NBURN=3000 NITER=25000 PRINT=10 NOABORT NOPRIOR=0 FNLETA=0 ISAMPLE_M1=2 ISAMPLE_M2=2 ISAMPLE_M3=2 IACCEPT=0.4 SEED=231457 FILE=Bayes.ext ​The first two estimation methods run successfuly with a convergence, but when it comes to BAYES, an error message always occurs: ​ OBJECTIVE FUNCTION IS INFINITE. PROBLEM ENDED 1THERE ARE ERROR MESSAGES IN FILE PRDERR ​I put safety brakes in the code to prevent ​0**power or square root of negative values, but the problem still occured. Setting lower and upper bound of the initial estimation, but it did not help either. I am wondering if anyone here encountered this issue previously? It seems quite strange to me that SAEM and IMP could succeed, but BAYES fails. Could you please let me know of the possible reasons behind this? Thanks very much. Best Regards -- Xinting