Internet Explorer cannot download 8080&type=http

I have a portlet which calls a jsp passing the certain parameters. This JSP generates a report in a PDF format.

When I issue the request separately directly hitting the JSP page (i.e. without going through the portal gateway) the PDf page is properly displayed but if I go through the portal gateway I get the following error,

Internet explorer cannot download 8080&type=http from sdb08.dev.uk

[423 byte] By [Srinivasan_Shridharan] at [2007-11-25 19:29:56]