Why do we get this error in Person Management when trying to change employee hours?

Summary:

In Person Management a few of us have tried to Change Hours but get this same error PER-1503231. I have checked and all data is present in the employee record.

Content (required):

When an employee changed their hours we wanted this reflected in Person Management, Change of Hours but get the same error each time. I have tried some other actions such as Change Manager and Change Assignment, Transfer and they all come up with errors. Can someone please help? Thank you

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