If you encounter domain separation issues, review this list of solutions.

Error or symptom Solution
A domain sys_id points to a non-existent domain This error occurs when a data record, such as a user or task record, has a sys_domain column value whose sys_id does not exist in the current domain table. The domain sys_id could have been accidentally deleted or it could refer to a previous domain table if you changed the domain table.
To fix the error, open a list for the table containing the error, filter on the invalid sys_domain value. Then, either manually enter the correct sys_domain value or remove it.
Note: You can have invalid domain sys_ids in any table that references the domain table. For example, invalid domain IDs can occur in the User Visibility Domain [sys_user_visibility], Group Visibility Domain [sys_user_group_visibility], and Contained Domain [domain_contains] tables.
A domain path or domain number sys_id points to the wrong domain This error occurs when a domain number or domain path query is out of sync with the actual domain name. This error can occur with domain numbers when adding domains requires renumbering or during the conversion from domain numbers to domain paths.

To fix the error, check the results in the Domain Separation Center. If the error persists, you can manually edit the value for the sys_domain_path or sys_domain_number columns to point to the proper domain.
The domain tree structure is corrupt This error occurs if there is a series of domain contains relationships that create an infinite loop among domains.

To fix the error, open a list for the domain table and manually edit the domain contains values to not form a loop.