Bishops Food order web form fails

[subasant]

On Chrome, Edge, and Safari, every single time I hit 'Submit' or 'Save' on an online Bishops Food Order form, it fails. The following error appears each time.
"ISV code reduced the open transaction count. Custom plug-ins should not catch exceptions from OrganizationService calls and continue processing."

I've wasted more than 5 hours testing and trying different browsers and selecting different options. Would appreciate any help/fix