I'm getting access error for website_mail.message_thread. It worked for some time and then it just stopped.

The error that I get:

AccessError: (u'The requested operation cannot be completed due to security restrictions. Please contact your system administrator.\n\n(Document type: mail.message.subtype, Operation: read)', None)

Error to render compiling AST
AccessError: (u'The requested operation cannot be completed due to security restrictions. Please contact your system administrator.\n\n(Document type: mail.message.subtype, Operation: read)', None)
Template: website_mail.message_thread
Path: /templates/t/section/ul/t[2]/t
Node: <t t-set="messages" t-value="object.message_ids.filtered(lambda m: m.subtype_id.internal == False)"/>

What security options needs the user to have to not throw this error? The messages are from a projects task.

On the website are displayed the tasks where the user is the customer and added as a follower.