Performance Documents - Error when trying to open a document

Summary:

From Performance Documents page, when we look for a document of an employee and click on it, we get an error.

Content (please ensure you mask any confidential information):

When we go into My Client Groups --> Performance --> Performance Documents, we look for a Document assigned to an employee, and when we click on it we get this error:

This error appeared just today and we are trying to add privileges to the HR to let him view the documents, but nothing works.

Does anyone know which privilege grants the user the chance to see the documents? If not, is this a profile option issue?