ISA 2006, Sharepoint 2010 giving HTTP 500 internal server error on HTTP Filter

Recently when playing around with the Sharepoint 2010 beta I extended a site to use Forms and passed that through ISA 2006.

This is all very basic stuff, there are a number of good references on how to set this up, but what I did not expect was the http 500 internal error on my browser (see below).

The solution was to modify the HTTP filter (egad! an error message that actually gives the correct problem!) within ISA for that Rule (right-click the rule and select "Configure HTTP") and uncheck "Verify normalization" (see image below). I do not know if this is restricted to Sharepoint, but I suspect that will all the razzle-dazzle that SP2010 is trying to pull off it is tripping over the big feet of ISA...