I've been creating quite a few custom symbols, and occasionally when I export the symbol as a .s01 file, I get the "Parameter is not valid" error message I pasted below.  The .s01 file is created, but it appears in the Symbol Browser as a red X (the 2nd image I pasted below).  If you would like me to send the original .s07 file via email, please let me know.  Thanks.