IE error “Url Too Long” isn't returned

[M!hrap]

I've been trying to identify a problem with an Ajax function that's sending large amounts of text to an ASP page. I believe the problem to be that when lots of text is entered into a form/input and the data is sent via Ajax, this results in a very large 'querystring'.The server returns the error "Url Too Long". However, I have tested this application on two different computers - both running IE8 - and on one of them, executing the same request returns nothing at all. So my question is, does anyone know how this error/feedback could be switched off? I'm guessing it's not a server setting as both computers are accessing the same application. I've tried turning off "Show friendly HTTP error messages" on the suspect computer but this hasn't helped.