Im accessing an autodiscover site behind an ISA 2006 firewall.

I login using FBA on the FW and behing i use Integrated.

When I access the site I get 600 Invalid Request. 

Can somebody help me - please ask for more info as this is not a lot but i dont know what else is needed.

If you are getting prompted for authentication, and then getting the "600 Invalid Request" response then this typically means Autodiscover is working ok.  If you want to verify that you have everything setup ok, do a "test autoconfiguration" from Outlook or use the remote test tool from Microsoft (https://www.testexchangeconnectivity.com/).

Yes - the fault is that it cannot resolve the user in exchange, but that is a seperate topic :)