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

20160216 lookup control error

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.

20160216 xml comparrison

The solution was to simply add the missing >8< row so that LookupTypes section now looked like this:

 

<LookupTypes>
  <LookupType id=00000000-0000-0000-0000-000000000000>8</LookupType>
  <LookupType id=00000000-0000-0000-0000-000000000000>9</LookupType>
</LookupTypes>

 

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.