Exchange 2010: Cannot download Offline Address Book. 500 - Internal Server Error

The problems with downloading an Offline Address Book are very common and can have many sources. If you can't download the OAB using the Outlook 2007 or Outlook 2010 this article may be useful for you.
Problem description
When you try to download the OAB using Menu Tools -> Send/Recive -> Download Address Book you don't see the name of OAB in the drop down list.

Diagnostics
Firstly you have to check if the Autodiscover is configured properly. You can use a Test E-mail AutoConfiguration wizard (Hold CTRL and right click the Outlook icon in the System Tray). You should see the list of URL addresses.

1. If the Autodiscover return an error you have to configure this service correctly (the configuration of the Autodiscover is out of scope of this article)
2. If the XML is displayed you need to find the OAB URL that looks similar to: https://yourservername.yourdomain.tlddomain/oab/guidnumber. Notice: The OAB address can be found in both "Protocol: Exchange RPC" and "Protocol Exchange HTTP" sections. The first one is for internal clients who are accessing the OAB from LAN and the second is for external clients who are accessing the OAB from the Internet.
3. If one of the OAB URLs is empty or wrong, correct the configuration using set-OABVritualDirectory cmdlet.
4. If everything is right then copy the OAB URL and try to open it using your Web Browser
5. You probably will see the error 500 - Internal Server Error (Figure 1)

Figure 1

In this situation check the following settings:

1. Is the Web-Based distribution enabled? Organization Configuration -> Mailbox -> Offline Address Book tab -> display your OAB Properties -> Distribution tab -> Enable Web-Based distribution must be enabled. There has to be at least one Client Access Server on the list. If the settings are correct go to the next point.
2. Using IIS Manager Console check if an OAB subfolder exists and contains a folder which name is a GUID. You should see a lot of files in this GUID subfolder. Check this on each CAS.
3. Have you created the redirection to simplify the Outlook Web App URL, like in this article http://technet.microsoft.com/en-us/library/aa998359.aspx? If yes go to the next point.
4. Did you remove the redirection from virtual folders? If yes go to the solution.

Solution

When you configure Http Redirection a web.config file is created in the OAB directory. This file has incorrect permissions. Assign Read and Read & Execute permission to Autheticated Users group then restart IIS using iisreset /noforce.
Now you can try to download the OAB using Outlook. It may be required to download it twice because sometimes the name of the OAB doesn't appear at first try.

Notice: When you are trying to open the OAB URL from Web Browser you will get "403 - Forbidden: Access is denied" error (Figure 2). This is normal. Your OAB is configured properly.

Figure 2

[Update 31.08.2016] Ken reported that it might take a little while to start working. He got 'object not found' error on first couple of tries after applying the solution.