We have noticed that we can’t open external reports (Tableau) in viewer, following error appeared: "This content cannot be displayed in a frame. To help protect the security of information you enter into this website, the publisher of this content does not allow it to be displayed in a frame."

Issue may be caused by Clickjacking protection in Tableau Server, you can read bout it here http://kb.tableau.com/articles/knowledgebase/clickjacking-protection. Disabling Clickjacking protection can fix the issue.

You need to follow Step 2 from article http://kb.tableau.com/articles/issue/error-this-content-cannot-be-displayed-in-a-frame:

1. On the computer running Tableau Server, open the command prompt as an administrator.

2. Navigate to the Tableau Server bin directory:

    cd "C:\Program Files\Tableau\Tableau Server\<version>\bin"

3. Run the following commands, in order:

    tabadmin stop
    tabadmin set wgserver.clickjack_defense.enabled false
    tabadmin config
    tabadmin start