Could anyone help me with this dynare mod file

i write a dynare file as follows. the problem is when i use mode_compute=4 to estimate the code, the error is :

??? Error using ==> chol
Matrix must be positive definite.

Error in ==> metropolis_hastings_initialization at 52
d = chol(vv);

Error in ==> random_walk_metropolis_hastings at 43
ix2, ilogpo2, ModelName, MhDirectoryName, fblck, fline, npar, nblck, nruns, NewFile, MAX_nruns, d ] = …

Error in ==> dynare_estimation_1 at 940

Error in ==> dynare_estimation at 62

Error in ==> Liu_replica at 296

Error in ==> dynare at 102
evalin(‘base’,fname) ;

could anyone figure out the reason? and another thing,when i use mode_compute=6 to estimate the code,the code can be estimated,but the result is not same every time. what is the different betweenmode_compute=6 and mode_compute=4?
data.m (5.2 KB)
code.mod (3.04 KB)

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