#error (C# Reference)
#error lets you generate an error from a specific location in your code. For example:
#error Deprecated code in this method.
Remarks
A common use of #error is in a conditional directive.
It is also possible to generate a user-defined warning with #warning (C# Reference).
Example
// preprocessor_error.cs
// CS1029 expected
#define DEBUG
class MainClass
{
static void Main()
{
#if DEBUG
#error DEBUG is defined
#endif
}
}