It could be a corrupt cached file.
Most browsers use a trick to make the internet seem quicker than it actually is, they do this by making a local copy of the pages you browse to, every time you make a request for a page your browser checks these cached files and if a copy exists it loads the local copy which is quicker than downloading the one on the internet.
For static pages that donít change this is great but for dynamic pages it can be a real pain so programmers generally send a self-destruct or expiration time with dynamic pages. The browser checks to see if the file is out of date and goes back to the internet if it is. The problem is that sometimes the file gets slightly corrupt and the expiration date isnít registered correctly so the browser keeps loading the corrupt local file. Another problem is that your browser can be set to never check for new pages, just to complicate things thereís a version of Internet Explorer (an early release of IE5) that when set to automatically work out whether to check for a newer file never does. You can get around this by setting your browser to ALWAYS check for newer files by selecting EVERY VISIT TO THE PAGE.
In IE itís in tools\internet options\settings.
I have my browser permanently set like this, with a fast connection the speed difference is nominal.