I am having the same issues getting that error on a form. It occurs when I click to add a new record to a child list, that is setup and working properly with the vLookup plugin otherwise (displays related items). I also have several other child lists connected, and I am able to add a new child record, with the lookup pre-populated as well. All work fine but this one list. The only column I have connected is a SP Lookup column (site content, using ID).
I looked at the child list (Task Type) and the Lookup column is present when I click on content types (in the settings menu). It was not listed as a source however, unlike the other out of the box fields for a Task list. So I have since made the lookup a site column, and then added it to the content type (Tasks). I deleted the old lookup from the child list, and added it back in from said content type. The error persists back at the parent form. Please help.
