After I click this irritating error box 13 times (it's always that exact number) then the box disappears and I can view all my emails correctly. I get this similar error on IE 7 as well but there it disappears in 2 times only. I tried different browsers, cleared cookies, different machines, different operating systems but in vain. Other friends were able to access the account just fine so I was wondering. Finally, I googled the error code and found the solution at Gmail Help Center. Basically, the solution is to access the account through secured interface available at https://mail.google.com. Now, I could not find any explanation of the problem but the proposed solution indeed got rid of the popup.