[Gretl-users] error message:criterion is not met a warning

Hi everone, I am new to gretl, i want to use its MLE for estimation. I have written small script just to check that how MLE works but i have following error message (criterion is not met a warning ). I have used sample data set data 2-1.gdt. here is my scrpit. genr pi=3.14 scalar a=2*pi scalar mu=1 scalar sigma=1 series s=sigma^2 sereis sq=2*s series s3=sigma^3 scalar sq3=2*s3 series c=vsat-mu series sq1=c^2 mle logl=-0.5*log(a)-log(sigma)-(sq1/sq) deriv mu=-c/s deriv sigma=-1/sigma + (sq1/s3) end mle i do not know where is the problem and if I use this code then i have error message that "*failed to invert OPG matrix GG'"* genr pi=3.14 scalar a=2*pi scalar mu=1 scalar sigma=1 series s=sigma^2 sereis sq=2*s series s3=sigma^3 scalar sq3=2*s3 series c=vsat-mu series sq1=c^2 mle logl=-0.5*log(a)-log(sigma)-(sq1/sq) params mu sigma end mle or if i add at last end mle --hessian error message will be "*numerical hessian is not computable*" Can anyone tell me about this error or how to solve it?? Thanks in advance. -- Haider