I had this error message recently in one of our designs. I was unable to determine the exact cause, but I did trace the problem to the symbol referenced in the pstxnet file. If you open the pstxnet file in excel, and scroll down to the line in question, you will see something like this.Originally posted in cdnusers.org by Hpattie
611 NODE_NAME R896 2
Look at the part properties on the component, in this case R896, to see if there are illegal characters in any of the fields. You could also try replacing the symbol from a known good library.