I would look at HTTP DATA LIST instead. You can view details on what errors occurred and see what URLS were responsible. Sort by response code (descending order by double clicking the header "response Code") and you will quickly see an 400 or 500 errors which need to be investigated. Also look for reply size of 0 as this usually indicates an error of some sort.
I tried that and still I can see the error graph but in my HTTP DATA LIST there were no Response Codes with 400 or 500 also there was no reply size of 0. I have attached the Excel sheet along with my reply. I will try to explore this issue further by Filtering URLS in the HTTP error graph and will post any information in case I find sumthing useful
Probably I might get an clue from filtering.
Quality Assurance Lead, India
"A Cat looked at the mirror and what she saw was a Lion. Secret of success depends on how you see yourself."
Apparently, http://tbt/images/pg_Title.jpg can't be found. Just comment it out of the script and your errors should go away. If you don't want to comment it out (effects will be minimal) you can find out why it no longer exists and address the issue on server side (probably not worth the effort).