In USS the message 'Required Fields Missing' is presented when required fields in the Dataasource are blank or when contextual information around a stored file (.pem, .key, or .p12) is incorrect. When you get the information while trying to upload a new file, I have had to manually copy a fresh version of the files to $USS_HOME\OSOP\shared\aquila_temp and then uploading the same certs through the USS UI. This process has to be repeated for every server that is having the same issue. I am able to verify the functionality of the updated data source via the Test Connection button. No restart of the service was required. I have gotten in to this situation when removing or applying patches to USS, and this issue may or may not cause a disable of a datasource.