Getting Error: Access Denied when a user opens EP

When you have a new EP install and haven't setup yet the users for accessing the site, you might come across this: Error: Access Denied. This is very easy to fix.

As an administrator of the site just open the EP site, go to Site Actions -> Site Settings-> Site Permissions and do a Grant Permissions for every user that you want to have access to the EP; be sure to select the proper rights (in most case read should suffice, but some may require the full or design if they want to change the pages, deploy web controls, etc).