Exception of type 'System.PlatformNotSupportedException' while downloading file.

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ASP.NET

web

web_development

Dear All

I am writing code for download image file.

Response.AppendHeader();
Response.ContentType=type;
Respone.WriteFile(file);
Response.End();

This is working for .gif,.jpeg,.png but it is giving problem for 'tiff'. I have try ContentType "image/tif" &"image/tiff" but it is giving error Headers

'Page.Response.Headers' threw an exception of type System.PlatformNotSupportedException'	System.Collections.Specialized.NameValueCollection {System.PlatformNotSupportedException}.

I have also tried for changing app pool to integrated but still it is not working.
I am using Classic 2.0 app pool & iis 7.0.
I have got temporary solution. As I remove update panel it works fine.
Can u tell me why this is happening?

Thanks