C# MarshalAs a String property

See more:

C#

I need to Marshal a string property so that I can pass it to my dll.

This is what I've got so far but it doesn't work, error is can't read or write protected memory when I attempt to pass it.

Doesn't allow me to pass with UnmanagedType.ByValTstr.

Note: I've managed to pass my string successfully as a field but not property.

public string firstName { 
           
     [return : MarshalAsAttribute(UnmanagedType.BSTR, SizeConst=51)]get {
            return _firstName;
      }
     [param : MarshalAsAttribute(UnmanagedType.BSTR, SizeConst=51)]set {
            _firstName = value;
      }
}