Why do I get the error message ‘Compiler Error Message: CS1595’

This problem occurs because the C# compiler does not have permission to access the folders in the path to the mscorlib.dll assembly

To resolve this problem, modify the compiler definition for the C# compiler to include the /nostdlib option. The /nostdlib option prevents the import of the mscorlib.dll assembly, which defines the entire System namespace.
To include the /nostdlib option in the C# compiler definition on a computer, follow these steps:

1. Open the Machine.config file, and then locate the section.
   
2. In the definition for C#, add the compilerOptions attribute with a value of /nostdlib.
   For example:

   
   <compiler language='c#;cs;csharp'
            extension='.cs'
            type='Microsoft.CSharp.CSharpCodeProvider, System,
            Version=1.0.3300.0,
            Culture=neutral,
            PublicKeyToken=b77a5c561934e089'
            warningLevel='1'
            compilerOptions='/nostdlib' />
   

   For more details refer PRB: ‘Compiler Error Message: CS1595’ Error Message When You Use the C# Compiler to Compile an ASP.NET Resource