Website configured in Plesk is not accessible: 500 Internal Server Error: Config section already defined

Symptoms

• Website configured in Plesk shows:

  PLESK_INFO: 500 Internal Server Error

• An attempt to reconfigure the website fails:

  C:> plesk repair web example.com
  Repairing web server configuration
  Repairing web server configuration for the domain example.com ….. [FAILED]
  – Filename: ?D:Inetpubvhostsexample.comhttpdocsweb.config
  Line number: 8
  Error: Config section ‘system.web/compilation’ already defined.
  Sections must only appear once per config file. See the help
  topic for exceptions

• Accessing IIS > Sites > example.com > ASP results in error message:
  

Cause

Duplicate section in the domain configuration file.

Resolution

1. Log in to Plesk
2. Go to Domains > example.com > File manager and open web.config file:
   

3. Remove or comment out the duplicate section mentioned in the error message:

   <compilation debug="true" targetFramework="4.0"> 
    <assemblies> 
    <add assembly="Microsoft.Build.Framework, Version=4.0.0.0, Culture=neutral, PublicKeyToken=************" /> 
    <add assembly="System.Management, Version=4.0.0.0, Culture=neutral, PublicKeyToken=************" /> 
    </assemblies> 
    <buildProviders> 
    <add extension=".rdlc" type="Microsoft.Reporting.RdlBuildProvider, Microsoft.ReportViewer.WebForms, Version=10.0.0.0, Culture=neutral, PublicKeyToken=***********" /> 
    </buildProviders> 
    </compilation>

4. Connect to the server over RDP

5. Open Windows command-line and reconfigure the domain:

   C:> plesk repair web example.com