Exactly the same problem. Solved with this: Upgrade to OJS 3.1.1.4 - The current role does not have access to this operation
Try adding the following to /lib/pkp/controllers/tab/settings/AdminSettingsTabHandler.inc.php (line 37)
$this->addRoleAssignment(ROLE_ID_SITE_ADMIN,
array(
‘showFileUploadForm’,
‘uploadFile’,
‘saveFile’,
‘deleteFile’,
‘fetchFile’
)
);