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What this message is telling you is that you have started to write something to the response in your JSP prior to the <logic:forward> tag, and that is not allowed. The <logic:notPresent> block that you have shown us must go at the very beginning of the JSP before writing anything -- even before the <head> block.
I'm afraid you simply can't do what you're trying to do in this way.
Tiles takes several page fragments and of those fragments, generates a single http page to send back to the browser. The principle behind a redirect is that you decide "up front" that this is not the page you should be displaying, but some other page. If you try to do this inside a tile (which, remember is a page fragment) you have already tried to send part of your response to the browser. You can't change your mind in mid-stream.
I haven't used tiles a lot, so don't know all the tricks, but here is something I think would work:
Put the following code in your postrfq.jsp:
and remove the <logic:notPresent> block from rfqpost.jsp.