user shared mailbox convert to a regular mailbox, permission problem sharepoint.

Hello,I have a user who stoped working in my company and I created a shared mailbox. Now he come back to the company and I have converted his shared mailbox to a regular mailbox, assign license, etc

The problem is that he is unable to access to sharepoint site folder through link only when he already had access permissions before to convert his mailbox.

Does anyone know what can happen?

---

Roberto