Your user does not have admin rights. It is of a standard user type and you are not allowed to access the folder you are trying to view: 1. Because it is a system folder or 2. The administrator restricted the access to the folder
Yeah there is a advanced permission that can be set to deny. This is just an example scenario. By default though non operating system drives are mounted with fairly open access.
Corruption in the operating system can cause all sorts of random issues, malware or someone that administers the system could change the default permissions for fixed and removable drives.