CRM 2011 not rendering on the browser, inspite of opening in the compatibility View

Even after compatibility view, the CRM 2011 doesn't open, on load- and opening the debugger says "mainscript is undefined"

One of the scenarios this would happen if the Main Folder of the CRM is secured and has no access provided to the User opening CRM.
To resolve this, navigate to the drive where CRM was installed , navigate to the main folder and select Security, provide Read access to the Users,