HiI had the same Issue. I'm using the proxy to access a FeatuerLayer hosted on a Spatial Data Server.I removed line 31 to 39 from the proxy.ashx because I don't need a token to access the layer.After that my proxy seemed to work. When I sent requests through the proxy and direct to the sds the data in the responses matched. The only difference I could find was in the header of the responses. So I added the following code to the proxy.ashx to append the Header of the response from the SDS to the response from the proxy.
//proxy.ashx
98: // append header attributes?!
99: for (int i = 0; i < serverResponse.Headers.Count; i++)
100: response.Headers.Add(serverResponse.Headers.GetKey(i), serverResponse.Headers.Get(i));
I don't know if it could cause other problems if the whole header is "forwarded" to the client. So I may try to figure out which attribute was missing and caused the problem.I know my setup is probably a little different. But this solution might help someone else.