Some members on my website complained about viewing some messages. I searched the problem here and then on the internet but just can't find any answers.

Even as the admin I faced the same problem.

When I view all the messages on one page (after I log in), I can't see one of the member's message instead it says "you have to become a member to view this message"

People who complained about this are already member. Since it happened to me and I'm the admin I can't think of any reason. I checked the permissions but nothing seems to be changed.

can you pls help?