1) Locate the instanceconfig.xml file at the location:
Update the instanceconfig.xml file to add the highlighted entry within the "security" tag (possible values are 'allow', 'prohibit' and 'sameDomainOnly'):
<!--This Configuration setting is managed by Oracle Business Intelligence Enterprise Manager-->
Now, this will only get you half way. You'll still run into the error, which really doesn't help you any. The 2nd piece is as follows:
2) Edit the 'web.xml' file at the following location:
Add the following highlighted entry to the file. The syntax is the opposite of what the syntax for instanceconfig.xml is, since the 'never' means to never block the rendering within IFrame (you can choose 'never' to always allow rendering in the IFrame, or 'differentDomain' to only allow rendering if it is in the same domain).
3) Now that you've completed both steps, restart the OBIEE System Components using opmnctl (Stop opmnctl and Start opmnctl). If you need to find this, you'll find it in your start menu on the server under the 'Oracle Business Intelligence' folder, called 'Stop BI Services' and 'Start BI Services' respectively.
4) Before testing, be sure to clear your browser cache.