[R] data.frame error using sem package

[Suzanne Witt]

I keep getting this error when I try to use the sem package.  I and  
another person who has successfully used the sem package for similar  
analysis (fMRI effective connectivity) cannot figure out what is  
wrong with my code.  I would appreciate any suggestions.

The error message:

Error in data.frame(object$coeff, se, z, 2 * (1 - pnorm(abs(z))),  
par.code) :
     arguments imply differing number of rows: 6, 0
In addition: Warning message:
Could not compute QR decomposition of Hessian.
Optimization probably did not converge.
in: sem.default(ram = ram, S = S, N = N, param.names = pars,  
var.names = vars,


Thank you,

Suzanne