Proper filter recording settings for .Net protocol v 11.52

Hello,

I am trying to record a .net (4.0) client-server application with VuGen and encountering an issue.  The following appears in my script: 

#warning:  Code Generation Error
// Found an undefined object of type System.IO.StreamReader. Assigning it the name reader_1.
// Suggested solution: adding both this type, in assembly mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089, to the filter 
// and/or any other types that return instances of this one.
// Note:  This script will not compile as is.

If I tried to create a custom filter and add the reference to System.IO in the filtering dialog, but it gives me an error. (attached)

I've tried reading through the best practices doc, located here: NET_Protocol_Filter_BestPractices

Any suggestions on how to resolve the needed reference??

Thanks,

Mark