[R] data.frame error using sem package

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

[R] data.frame error using sem package

I am trying to use sem to measure effective connectivity among four brain regions. I have pasted the code that I am trying to run since that seems easier than trying to come up with another example. The input data is time series data taken from SPM; they are each 1x121 columns of numbers.