Check if output image exists

[spencermartin]

I'm using a mapservice to run a javascript site. Using the exportMapImage from the ArcGISDynamicMapServiceLayer the url will sometimes return a url that appears to be a valid url and points to a png file in the output folder but the image does not exist.  Why or how does it return what appears to be a valid url for the image but the image was never created?  I either need find a way to either return an empty url or figure out why the image is not getting created.

[RaviNarayanan]

Does this behavior always happen for the same service or happens once in a while?

If it happens all the time for specific service, it could be that the virtual directory is not configured correctly. The output directory could be different from the one configured in the virtual directory.