R – upgrade an ASP.NET web service to WCF and still call it from ASP.NET 1.1

What's likely happening is that SignalData is indirectly changing the subscribers dictionary under the hood during the loop and leading to that message. You can verify this by changing

foreach(Subscriber s in subscribers.Values)

To

foreach(Subscriber s in subscribers.Values.ToList())

If I'm right, the problem will disappear.

Calling subscribers.Values.ToList() copies the values of subscribers.Values to a separate list at the start of the foreach. Nothing else has access to this list (it doesn't even have a variable name!), so nothing can modify it inside the loop.

Yes.

Here's an article with the same question and an answer on how you would do it.

FTA:

If you use a basicHttpBinding

 <endpoint address="basic"
  binding="basicHttpBinding"
  contract="YourNameSpace.IYourService" />

You are telling WCF to use SOAP1.1. This is what ASMX used in ASP.NET 1.1 and 2.0. The Add Web Reference feature of Visual Studio 2003 and 2005 reads the definition of the SOAP web service using WSDL. You can enable WSDL on your WCF Service by including a serviceBehavior with httpGetEnabled for serviceMetaData

You would do this by adding a behaviorConfiguration to your service

<service name="MyService" behaviorConfiguration="MyBehavior">...
</service>
...
<behaviors>
<serviceBehaviors>
<behavior name="MyBehavior">
<serviceMetadata httpGetEnabled="true"/>
</behavior>
</serviceBehaviors>
</behaviors>

Then you can browse to the HTTP hosted WCF Service using Add Web Reference to create the client proxy, or if you need more flexibility, you can use wsdl.exe(from 1.1 or 2.0) from commandline.