SortInfo is a great little proggy, but I don't know that it's been updated since winMAME became the standard build.
I usually end up running it from a listinfo file as follows (from the Sinfo documentation):
"If you can't import from MAME then make a listinfo file by running MAME with the following command line: "MAME -listinfo > listinfo.txt". MAME should then make a file named "listinfo.txt" and that one can be imported as a "List Info File"."
Once you build the file, you select "File - Import - ListInfo file" and then tell the program where the file is located.
Post a followup if this fails, and I will see if I can suggest anything else.