I'm pretty sure it happened after the last Hero Lab update. At the same
time, the 3E stock portfolios developed a reliance on the Supernatural
handbook. I can confirm that the portfolio and stock files I wrote up from
before the update do not bring this error up.
If you're looking for an easy fix, on the 3E files, I unzipped the
portfolio, did a text replacement to remove that item in the XML files,
then zipped it back up. You could probably write a utility to automate the
process.