Publish 3.20 on GoDaddy only connects tp ErrorPage.htm instead of nopCommerce install page

I have followed the publish instructions (use release config, rebuild entire solution, deploy nop.web project) using web deploy to publish nopCommerce 3.20 to GoDaddy and used GoDaddy File Manager to give full permissions to Administrators, System, Plesk Domain user, Plesk IIS Worker Process Identity Account, and Application pool group for directories App_Data, Content, Plugins, Themes and file Global.asax and tried to open the site expecting the nopCommerce install page instead I get nopCommerce's ErrorPage.htm the browser address bar shows http:// <my website>/ErrorPage.htm errorpath="/". I can see nothing in the GoDaddy logs so I am a bit stumped. Any help/pointers will be greatly appreciated.

To find out what went wrong you need to turn off the custom errors mode.

1. Open web.config file
2. Find out the following line <customErrors defaultRedirect="errorpage.htm" mode="RemoteOnly">
3. Replace it with <customErrors defaultRedirect="errorpage.htm" mode="Off">

Thanks for your usual prompt reply and help. I have done as you instructed and know get the following:

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Server Error in '/' Application.

Security Exception
  Description: The application attempted to perform an operation not allowed by the security policy.  To grant this application the required permission please contact your system administrator or change the application's trust level in the configuration file.

Exception Details: System.Security.SecurityException: Request for the permission of type 'System.Security.Permissions.ReflectionPermission, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089' failed.

Source Error:

An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below.  

Stack Trace:

[SecurityException: Request for the permission of type 'System.Security.Permissions.ReflectionPermission, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089' failed.]
   System.Delegate.DelegateConstruct(Object target, IntPtr slot) +0
   AutoMapper.Internal.ProbingAdapterResolver..ctor(String[] platformNames) +36
   AutoMapper.Internal.PlatformAdapter..cctor() +184

Version Information: Microsoft .NET Framework Version:4.0.30319; ASP.NET Version:4.0.30319.34212
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It would seem I will need to contact GoDaddy support to grant the required permission, unless you can tell me different, perhaps the configuration file refered to is web.config? Any extra help/info you can give me for when I contact GoDaddy support would be appreciated.

After a bit of digging I have found that this is the Code Access security Setting which defaults to medium on GoDaddy and needs to be changed to Full. Having done this I now get the install screen. As I have a database already uploaded to GoDaddy I will now put in place Plugins.txt and settings.txt and see how I get on. Thanks again for your help Andrei, most appreciated.