Validation Errors While Saving Record(s) "There were custom validation error(s) encountered while saving the affected record(s). The first validation error encountered was "Lookups on activites must have a unique domain. You can not have multiple relationships to the same object."

I don't have any existing lookup field to the Lead object from the Activity object. So I'm not sure what's causing this error. I was able to create a Contact lookup field without issues, but when I create one for the Lead object, it spits out this error.

EDIT: I found the problem. I changed the UI to Classic, went to the Activity object's field and relationships page, and found the Deleted Fields link. In there, there was a lead lookup field. I deleted that and created a new lookup and everything was squared away.

1 Answer 1


Here are two articles talking about Lookup Relationships on Activities in SFDC.



Both of them are slightly confusing, because they don't explain a main limitation very well. You can only have 1 lookup relationship on Activities, so you are forced to make that one relationship work for your org.

From your question, it appears that you may be trying to make a lookup relationship for the Lead and for the Contact on the Activity object. There is a field called WhoId that has the Id of the Contact, Lead, or User with limited Name object information. It's not the same as a full lookup field, but it can be helpful.

  • WhoId is the right answer for this use case
    – cropredy
    Commented Oct 28, 2019 at 23:48

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