Error: You cannot set a hierarchy field to point to itself or a child record

Scenario 1: Merging Accounts with a Circular Lookup Field

This error can occur when merging two Account records when a custom lookup field on the Account object points back to another Account:

• Account A has a custom lookup field that points to Account B.
• On the Merge Accounts wizard, the user selects Account B as the master record and retains the old value from Account A's lookup field (which points to Account B).
• After the merge, Account A is deleted and Account B is kept. However, Account B's lookup field now points to itself, which triggers the error.

Resolution: Before merging, update the custom lookup field on the non-master record so that it does not point to the record being selected as the master. Save the change, then proceed with the merge.

Scenario 2: User Hierarchy Field Circular Reference

This error can also occur when configuring a custom User hierarchy field (for example, a field called "Manager") when the assignment creates a circular chain.
Example:

• User A reports to User C (User C is User A's Manager)
• User C reports to User B (User B is User C's Manager)
• If you attempt to set User A as the Manager for User B, Salesforce will throw this error because User B would become the manager of User C, who is already the manager of User A — creating a circular chain.

Resolution: Before saving, ensure the user hierarchy field assignment does not create a loop. Review the existing hierarchy chain for the record before making changes.