The "500 Internal Server" error is mainly seen on Windows 2008 R2 servers with RA 9.0.161 and can be cuased by insufficient permissions for the IUSR windows account used by IIS.
Steps to assign the recommended permissions to the IUSR local account:
1. Open the Server Manager utility by right clicking my computer and selecting Manage.
2. Expand Configuration, then Local Users and Groups.
3. Select the Groups folder. Double click the Administrators group on the right.
4. Click Add and ensure that the Local field shows the local machine name vs the domain name.
If the domain name is displayed click on the Locations buttom and select the local machine name.
5. In the Object Names field type ‘IUSR’ and click the Check Names button . The local IUSR account should populate, Click the Ok button.
6. Click the Ok burron on the Administrators properties window.
7. Open a command prompt and type ‘iisreset’ for changes to take effect.