Upgraded ADF application (9.3 to 10.1) issues

Discussion created by tomfumb on Aug 1, 2013
Latest reply on Jul 2, 2015 by anmartin
I can't figure out which is the best sub-forum for this question (why are there so many?), and I suspect I might be the only person in the whole world attempting to do this, but here goes...

I had an application based on the .NET Web ADF originally built in 9.3. The server is being upgraded to 10.1 so the application needs to move with it (re-architecting is not an option).

The automated upgrade utility was not the smoothest process and I have since fixed a couple of very obvious bugs in the ESRI JavaScript. However there is one problem I can't figure out:

Intermittently, after a full page reload, the map fails to render. The application calls ESRI.ArcGIS.ADF.Web.UI.WebControls.MapHandler.ashx requesting a URL for the new map image. Sometimes that handler returns

{"code":400,"type":"error","errorMessage":"Resource <service name> not found"}

The application then requests an image from ESRI.ArcGIS.ADF.Web.MimeImage.ashx passing an ImgID parameter that seems to be randomly made-up - I can't see it in any previous requests and it obviously isn't provided by MapHandler.ashx. The server then responds with a 404. If I reload the application again the same requests are sent with exactly the same parameters (in the example I saw the post-reload request even passed the same 't' parameter which I assume should represent time) and a successful response is returned.

Can anyone tell me why my service is reported as unavailable? ArcGIS Server is not logging any errors or warnings.