Preemptive apologies for the rudimentary question, but I'm having trouble specifying correlated errors for a confirmatory factor model. It is possible that I am specifying them wrong, or that there is some problem with my model (I'm hoping it is the former). Currently, I am using a path specification, which indicates a double-headed arrow between my first and fifth indicator:
mxPath(from = c("ac1"),
to = c("ac5"),
arrows = 2,
free = T,
values = 1,
labels = ("cov15"))
But when I run the model, I get this message:
"Error: The job for model 'The AC Model' exited abnormally with the error message: Backing out of parameter space region where expected covariance is non-positive-definite."
1. I looked in the user guide, but can't find the answer - am I specifying correlated errors correctly?
2. What does this error message mean? Can I salvage this model?
Thank you in advance for any help you can give. I'm between a rock and a hard place because the correlated errors are an important part of my thesis, so they need to be in there somehow, but I can't seem to get the model to run.
PS - syntax for the whole model is attached, if you are interested.