I have a very old asp.net application where we are using window.showModalDialog for popups. The return value is always undefined when running from localhost (either using visual studio 2013 or deployed in IIS 7.0) but the same code when deployed in server (2008 R2), all the popups are returning values and is working fine. I do not have any error that I can paste here.
Tried running application using ip address and localhost.
I have looked at other links where they have an opposite issue - working in localhost but return value undefined in server.