SharePoint 2010 Visual WebPart gives 403 error to users

We have a Visual Webpart deployed to SharePoint 2010 with following key functionality

1. Access SQL DB
2. Access SP Groups to see if current user is part of few SP groups

This Web Part uses AJAX control toolkit.
Our SharePoint farms are scheduled to recycle App Pools over night.

Problem:
In the morning when a normal user access the page containing Visual Web Part, IE will show 403 error.
Once Site admin access the page the error will go away and normal users can access the page without any problem.

Solution:

·         Give Read permission for Everyone to \bin and \_app_bin folders

·         Copy AJAX Control toolkit dll to GAC

·         Add Authenticated users to group WSS_WPG