I can reproduce this issue using Nopcommerce 2.30 downloaded straight from your site with no modifications.
The issue is as follows:
A number of payment handlers require posting of data and redirection to another site (Worldpay, paypal, etc.). This is achieved by building a form and using the Post method of the RemotePost class to build up a HTML page and replace the current response with this html. When HttpCompression is enabled this does not work correctly and a blank page is displayed (0 bytes are passed back to the browser).
This issue can be simply reproduced by enabling httpcompression from the nopcommerce settings screen and modifying the Index action of the Home controller as follows (for testing purposes)
public ActionResult Index()
{
Response.Write("test");
Response.End();
return View();
}
The issue itself appears to be caused by the following lines:
if (acceptEncoding.Contains("GZIP"))
{
response.AppendHeader("Content-encoding", "gzip");
response.Filter = new GZipStream(response.Filter, CompressionMode.Compress);
}
else if (acceptEncoding.Contains("DEFLATE"))
{
response.AppendHeader("Content-encoding", "deflate");
response.Filter = new DeflateStream(response.Filter, CompressionMode.Compress);
}
Turning httpcompression off (or even commenting out these lines) will allow the response to be updated correctly, turning it back on will cause the error to occur again
