How do I determine why a webservice reference is being prevented from being added to my project in VS2008?

I have a VS2005 project that contains a couple web service references. The project has recently been upgraded to VS2008 but now there is a problem with the web references...probably because they may not have been upgraded properly.

When I select Update Web Reference I get the following error:

"Value cannot be null. Parameter name: discoveryError % mexError" which is very helpful.

I've then deleted the web reference with the intent of re-adding it...

The Add Web Reference dialog comes up and successfully loads information about each of the methods associated with the web service.

However, I can't add the reference as the button to do so is grayed out and there is a text box titled "Web services found at this URL:" which contains the text "Operation is not valid due to the current state of the object".

Now finally, this brings me to my main question... How then do I add this web reference? Or better yet, how do I find out what is invalid about the "current state of the object"?

Has anyone had a similar experience in VS2008?

From stackoverflow

• Finally figured it out.

  I used WebService Studio to give me a better idea of what was going on. It came back with the error message "The request failed with HTTP status 407: Proxy Authentication Required".... which let me know that I had to install the new security certificate...the old one had expired.

  I guess that answers this question about how to find more about what is invalid about the web service.

  Martín Marconcini : +1, thanks for that link

• Thanks a lot! solved!

  using the "WebService Studio".

• Hi I´ve just to receive the same error: with update reference from Visual Studio 2008

  "Value cannot be null. Parameter name: discoveryError % mexError

  I´ve already fixed it checking the project´s folder ACL list. Definelly, I needed to add IUSR to the folsder´s security... and that´s it! e

  I worked 4 me, and I hope to help anyone as well...