It looks like nuget package for version 2.0.4 contains a wrong version of the dll.
Steps to replicate the issue:
1) Download 2.0.4 source code
2) Add a simple console application to ExpressionEvaluator's solution with the following code in the main method
dynamic scope = new ExpandoObject();
scope.FirstName = new ExpandoObject();
scope.FirstName.Value = "Sebastiano";
var exp = new CompiledExpression("FirstName.Value");
var fx = exp.ScopeCompile();
3) Add ExpressionEvaluator as project reference to the newly created console application
4) Set the console application as startup project
5) Run console application
6) Observe the expression is correctly scope compiled and the application shows the value "Sebastiano" on the console
7) Remove ExpressionEvaluator project reference from the console application's references
8) Add ExpressionEvaluator as nuget package (latest stable 2.0.4) to the console application's references
9) Run the console application
10) Observe an exception is raised of type ExpressionParseException with the following additional information: Cannot resolve symbol "FirstName" at line 1 char 0
Using 2.0.3 nuget package, the console application runs correctly.
As running the application with 2.0.4 source code works, this is suggesting 2.0.4 nuget package is containing an older or faulty version.