Here is the error Solution
You can go to transaction PRMD and check if your employee has the IT 0001 created for 01/30/2007 if not you need to create it
Please try to use T.code PA30 to make changes to Org Assignment....since you haven't specified the issue completely, I guessing that you are using the Actions screen to make the changes. Hope it helps
You have not create the IT0001, that's why. How did you create the personnel number? Are you sure is created?
?You need to go to T.code PA40 and create it. Maybe you need to use the same Entry Action and move forward to without changing IT000 and create the IT0001.