Reporting services and custom library problem

Question

Greetings, I have a problem with reporting services and custom library I've created a custom Library:

public class MyClass{
public static string GetValue(string s)
{
return s.ToUpper();
}
}

Namespace is MyLibrary. I've added reference to reporting services. I've done everything what is described here: http://www.c-sharpcorner.com/UploadFile/balajiintel/CustomAssemblyinRS06302005081435AM/CustomAssemblyinRS.aspx however, it does not want to work. When I use Preview Mode it works fine. However when I run it the error is returned for my parameter named 'ReportCustomLibParameter' which is as follows

Error during processing if 'ReportCustomLibParameter' report parameter.

for this parameter I set default value as follows:

=MyLibrary.MyClass.GetValue("test")

What can be wrong here?