Problems with external access...

Recently, when exposing a SharePoint instance to the outside world using ISA server, I came arocss some very strange behaviour.

Basically, whenever doing things like adding a new item to a list, I would be presented with a HTTP error saying "Error Code: 500 Internal Server Error. The request was rejected by the HTTP Security filter." Interestingly, by shortening the URL (or so I thought), I would be able to access whatever resource I was trying to get to.

The issue turned out to be very simple. I noticed that by shortening the URL, I was actually removing special characters (I was cutting off things like &Source=.... &RootFolder=....). It turns out ISA blocks "high-bit characters" by default as a security measure, but this default setting messes up WSS / MOSS publishing as it uses these high-bit characters all the time.

The proceedure for turning this off is described in KB837865.

Hope this helps someone else from allot of headscratching :)