We are in the process of upgrading one of our clients from v2011 to v2016. When opening up a Contact form after the migration, users would see this error after clicking Save or when the form auto-saved:
LOOKUP CONTROL ERROR: Cannot add item of typename= to the lookup control
We noticed that the error was on the OwnerId field. So I decided to export out the customizations for the contact and also exported out the customizations for the lead entity (which had never been customized).
When I compared the two attribute definitions side-by-side, I could see that the contact’s definition was missing the ability for Owner to be a user. Oops.
The solution was to simply add the missing >8< row so that LookupTypes section now looked like this:
Once this change was imported back in and published, the problem was solved. We’re unsure of the cause – our support desk has seen it a few times over the years. The pattern *might* be that these clients originated from CRM v4.0 and were upgraded.
Hope this helps.