[R] problem in metro_hasting function‏

[hms Dreams]

Hello,
I estimated three paramters using non informative prior(all paramters following uniform distribution)
 
the output is:
Error in optim(pars, li_func, control = list(fnscale = -1), hessian = TRUE,  : 
  non-finite finite-difference value [1]
 
How can I solve it using uniform distribution for all paramters??
 
(the same code is working when I use informative prior When I sugessted other distriutions like gamma and exp.) 
 
Thank you
 		 	   		  
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