Invoking a tool using BSRE is a two step process.
First you invoke a normal BS layout tool, in which the only difference from a normal layout tool, is the RE icon.
Then, by virtue of clicking on the icon, you invoke the AA tools.
So in the first step you need to have your usual licenses for layout. It could be a layout or a layout high speed session.
If you have only a layout license and in the first popup window you will check the high speed option, you will get an error, because you need a layout high speed option.
In the second pop up window, it will ask you for AA licensing. So if you have autoroute or can check this. OR if you have high speed (HSR) you can check this.
This two steps are separated from each other. You may have the right licenses for Layout, but not for AA, or the other way around. Check with your system administrator which licenses you have or contact your trusted Mentor sales person for additional licenses.
Hope this helps