Search the forum. There are a variety of issues that can lead to this problem (most often there is an identifcation issue or the data do not match the observation equation). See e.g. [The hessian matrix at the "mode" is not positive definite!)
Search the forum. There are a variety of issues that can lead to this problem (most often there is an identifcation issue or the data do not match the observation equation). See e.g. [The hessian matrix at the "mode" is not positive definite!)