[SalesForce] Not able to open Visualforce page

Whenever you want to display a report chart in VisualForce page, the user should have appropriate permission to view the report as well.

Try the following:

• Take the report_id and go the report page as 'https://mydomain.salesforce.com/[report_id]'

• Edit the report and click on Save Properties

• Make sure you save the report into accessible public folder (like Unfiled Reports)

Once you refresh the VF page you should be able to see the report.

Update:

• The problem is you don't have any charts in the report to display

Add Chart:

• Click on customize on the report and click on Add Chart
• Save the report and come back here, you should be able to see the report

Its really weird that the message what it was displaying is mis-leading from what is really happening.

From the Spring '17 Release Notes on Allow CSRF Protection on GET Requests to Visualforce Pages (Critical Update):

When this option is enabled for a Visualforce page, you can’t access the page by entering its URL—/apex/PageName. Also, plain links to that page using tags don’t work. If you try to access a Visualforce page with CSRF protection enabled, the page doesn’t load and you get an error.

Plain links from a page with CSRF checks work, but links to the page do not. For example, if your page has the name PageName, the link Link doesn’t work. Instead, use the URLFOR() formula function, the $Page global variable, or the apex:outputLink component.

<apex:outputLink value="/apex/PageName">Link using apex:outputlink</apex:outputlink>
<a href="{!$Page.PageName}">Link using $Page</a>
<a href="{!URLFOR($Page.PageName)}">Link using URLFOR()</a>

CSRF [sic] checks on GET requests also affect how Visualforce pages are referenced from Apex controllers. Methods that return the URL of CSRF-protected [sic] pages for navigation don’t work:

public String getPage() {
    return '/apex/PageName'; 
}

Instead, use methods that return a reference to the Visualforce page instead of the URL directly.

public class customController {
    public PageReference getPage() {
        return new PageReference('/apex/PageName'); 
    }
    public PageReference getPage1() {
        return Page.PageName; 
    }
}

See also: Visualforce PageReference - Name Constructor vs. Factory