@LoneStar2911 - Thank you for the suggestion! I've replaced IGV with GridList and that fixed the problem.
@Sharlikran - "Why" is clearly because I didn't know better.
I don't know where the "outdated category" list is nor the Comments section. Minion doesn't show the add-on as deprecated so I thought I was golden.
"I am only an egg."
@Baertram - I didn't know what to look for in the forums. Now that you all kindly pointed out that the error referenced Inventory Grid View, I could see it listed in the error message text. I'm not a dev of any kind, though, so I would have been casting about blindly. It's still not apparent to me from looking at the error message that IGV was causing the problem.
End users ARE a PITA!!
Thanks to everyone for the swift responses and for your patience with my iggerance.
