This error occurs when SelectHR tries to save information into the database, but a required field, in this case User Number, has no value.
When SelectHR attempts to insert a NULL value, meaning the system has no user to record, the database rejects the action because the field is not allowed to be empty.
As a result, the save operation fails, and the workflow step ends with this error.
Error when requesting absence
One of the most common causes of this error is when a workflow tries to send an email to a user account that does not exist. This can happen if the intended recipient has been deleted, was never set up correctly, has no linked person record, or has become inactive without the workflow routing being updated.
When the workflow tries to record that user as an authoriser or message recipient, SelectHR cannot find their User Number. Because the User Number is missing, the system attempts to insert NULL into the @Authorisers table. Since the column does not allow NULL values, the entire workflow fails at that point.
After correcting the underlying data issue, you will need to ask the employee to start a new workflow.