我是一个初学者，最近在做农村企业社会责任，准备用结构方程模型。通过AMOS进行参数估计时总发生下列错误。


An error occurred while attempting to fit the model.
Either the constraints on the parameters or the initial parameter values are bad.This error
can occur, for example, if you request a maximum likelihood solution while specifying initial
parameter values that prevent the population covariance matrix from being positive definite.
Check to make sure that every endogenous variable has a residual variable(error variable)  
associated with it.

求高手解答是什么原因，谢谢了~