FAST Crawling Error HRESULT E_FAIL has been returned from a call to a COM component.

I got an error while start crawling from my content source by FAST Crawl
the crawl log said "Error HRESULT E_FAIL has been returned from a call to a COM component."

then I found an solution from the below link which is change the impersonate value in target content source web.config

http://www.sharepointben.com/blog/Lists/Posts/Post.aspx?ID=463

then rerun the crawling and it works.

but beware of the web.config impersonate value. if your web application is needed to be set to false. it gonna be an issue with your search component.

I got an idea for around on this. Let me take time to prove it and I'll update the result.