The following error displays in the debug console during a map draw operation:
MapHandler error message:
DrawImage returned error: No image data returned from server (Draw failed)
If the Map contains a graphics resource that is visible but all of its graphics layers are not, this error is returned by the MapHandler during a map draw operation.
When a non-cached ArcGIS Server resource is visible, but its layers are not, map draw operations, such as an extent change, requests a map image by way of the MapHandler. The map image is empty. For ADF graphics resources, a map image is not generated, but the error message is returned. While this raises concerns because the error is visible in the debug output window, the effect on a Web ADF application at runtime is negligible. From an end-user perspective, the Web ADF application still functions and there is no indication that an 'error' occurred.